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Psychology

Briefer Course

by William James  

PREFACE.

In preparing the following abridgment of my larger work, the Principles

of Psychology, my chief aim has been to make it more directly available

for class-room use. For this purpose I have omitted several whole

chapters and rewritten others. I have left out all the polemical and

historical matter, all the metaphysical discussions and purely

speculative passages, most of the quotations, all the book-references,

and (I trust) all the impertinences, of the larger work, leaving to the

teacher the choice of orally restoring as much of this material as may

seem to him good, along with his own remarks on the topics successively

studied. Knowing how ignorant the average student is of physiology, I

have added brief chapters on the various senses. In this shorter work

the general point of view, which I have adopted as that of 'natural

science,' has, I imagine, gained in clearness by its extrication from so

much critical matter and its more simple and dogmatic statement. About

two fifths of the volume is either new or rewritten, the rest is

'scissors and paste.' I regret to have been unable to supply chapters on

pleasure and pain, æsthetics, and the moral sense. Possibly the defect

may be made up in a later edition, if such a thing should ever be

demanded.

I cannot forbear taking advantage of this preface to make a statement

about the composition of the 'Principles of Psychology.' My critics in

the main have been so indulgent that I must cordially thank them; but

they have been unanimous in one reproach, namely, that my order of

chapters is planless and unnatural; and in one charitable excuse for

this, namely, that the work, being largely a collection of

review-articles, could not be expected to show as much system as a

treatise cast in a single mould. Both the reproach and the excuse

misapprehend the facts of the case. The order of composition is

doubtless unshapely, or it would not be found so by so many. But

planless it is not, for I deliberately followed what seemed to me a good

pedagogic order, in proceeding from the more concrete mental aspects

with which we are best acquainted to the so-called elements which we

naturally come to know later by way of abstraction. The opposite order,

of 'building-up' the mind out of its 'units of composition,' has the

merit of expository elegance, and gives a neatly subdivided table of

contents; but it often purchases these advantages at the cost of reality

and truth. I admit that my 'synthetic' order was stumblingly carried

out; but this again was in consequence of what I thought were pedagogic

necessities. On the whole, in spite of my critics, I venture still to

think that the 'unsystematic' form charged upon the book is more

apparent than profound, and that we really gain a more living

understanding of the mind by keeping our attention as long as possible

upon our entire conscious states as they are concretely given to us,

than by the _post-mortem_ study of their comminuted 'elements.' This

last is the study of artificial abstractions, not of natural things.[1]

But whether the critics are right, or I am, on this first point, the

critics are wrong about the relation of the magazine-articles to the

book. With a single exception all the chapters were written for the

book; and then by an after-thought some of them were sent to magazines,

because the completion of the whole work seemed so distant. My lack of

capacity has doubtless been great, but the charge of not having taken

the utmost pains, according to my lights, in the composition of the

volumes, cannot justly be laid at my door.

CONTENTS.

CHAPTER I.

                                                                    PAGE

INTRODUCTORY                                                           1

Psychology defined; psychology as a natural science, its data, 1. The

human mind and its environment, 3. The postulate that all consciousness

has cerebral activity for its condition, 5.

CHAPTER II.

SENSATION IN GENERAL                                                   9

Incoming nerve-currents, 9. Terminal organs, 10. 'Specific energies,'

11. Sensations cognize qualities, 13. Knowledge of acquaintance and

knowledge-about, 14. Objects of sensation appear in space, 15. The

intensity of sensations, 16. Weber's law, 17. Fechner's law, 21.

Sensations are not psychic compounds, 23. The 'law of relativity,' 24.

Effects of contrast, 26.

CHAPTER III.

SIGHT                                                                 28

The eye, 28. Accommodation, 32. Convergence, binocular vision, 33.

Double images, 36. Distance, 39. Size, color, 40. After-images, 43.

Intensity of luminous objects, 45.

CHAPTER IV.

HEARING                                                               47

The ear, 47. The qualities of sound, 43. Pitch, 44. 'Timbre,' 45.

Analysis of compound air-waves, 56. No fusion of elementary sensations

of sound, 57. Harmony and discord, 58. Discrimination by the ear, 59.

CHAPTER V.

TOUCH, THE TEMPERATURE SENSE, THE MUSCULAR SENSE, AND PAIN            60

End-organs in the skin, 60. Touch, sense of pressure, 60. Localization,

61. Sensibility to temperature, 63. The muscular sense, 65. Pain, 67.

CHAPTER VI.

SENSATIONS OF MOTION                                                  70

The feeling of motion over surfaces, 70. Feelings in joints, 74. The

sense of translation, the sensibility of the semicircular canals, 75.

CHAPTER VII.

THE STRUCTURE OF THE BRAIN                                            78

Embryological sketch, 78. Practical dissection of the sheep's brain, 81.

CHAPTER VIII.

THE FUNCTIONS OF THE BRAIN                                            91

General idea of nervous function, 91. The frog's nerve-centres, 92. The

pigeon's nerve-centres, 96. What the hemispheres do, 97. The

automaton-theory, 101. The localization of functions, 104. Brain and

mind have analogous 'elements,' sensory and motor, 105. The motor zone,

106. Aphasia, 108. The visual region, 110. Mental blindness, 112. The

auditory region, mental deafness, 113. Other centres, 116.

CHAPTER IX.

SOME GENERAL CONDITIONS OF NEURAL ACTIVITY                           120

The nervous discharge, 120. Reaction-time, 121. Simple reactions, 122.

Complicated reactions, 124. The summation of stimuli, 128. Cerebral

blood-supply, 130. Brain-thermometry, 131. Phosphorus and thought, 132.

CHAPTER X.

HABIT                                                                134

Its importance, and its physical basis, 134. Due to pathways formed in

the centres, 136. Its practical uses, 138. Concatenated acts, 140.

Necessity for guiding sensations in secondarily automatic performances,

141. Pedagogical maxims concerning the formation of habits, 142.

CHAPTER XI.

THE STREAM OF CONSCIOUSNESS                                          151

Analytic order of our study, 151. Every state of mind forms part of a

personal consciousness, 152. The same state of mind is never had twice,

154. Permanently recurring ideas are a fiction, 156. Every personal

consciousness is continuous, 157. Substantive and transitive states,

160. Every object appears with a 'fringe' of relations, 163. The 'topic'

of the thought, 167. Thought may be rational in any sort of imagery,

168. Consciousness is always especially interested in some one part of

its object, 170.

CHAPTER XII.

THE SELF                                                             176

The Me and the I, 176. The material Me, 177. The social Me, 179. The

spiritual Me, 181. Self-appreciation, 182. Self-seeking, bodily, social,

and spiritual, 184. Rivalry of the Mes, 186. Their hierarchy, 190.

Teleology of self-interest, 193. The I, or 'pure ego,' 195. Thoughts are

not compounded of 'fused' sensations, 196. The 'soul' as a combining

medium, 200. The sense of personal identity, 201. Explained by identity

of function in successive passing thoughts, 203. Mutations of the self,

205. Insane delusions, 207. Alternating personalities, 210. Mediumships

or possessions, 212. Who is the Thinker, 215.

CHAPTER XIII.

ATTENTION                                                            217

The narrowness of the field of consciousness, 217. Dispersed attention,

218. To how much can we attend at once? 219. The varieties of attention,

220. Voluntary attention, its momentary character, 224. To keep our

attention, an object must change, 226. Genius and attention, 227.

Attention's physiological conditions, 228. The sense-organ must be

adapted, 229. The idea of the object must be aroused, 232. Pedagogic

remarks, 236. Attention and free-will, 237.

CHAPTER XIV.

CONCEPTION                                                           239

Different states of mind can mean the same, 239. Conceptions of

abstract, of universal, and of problematic objects, 240. The thought of

'the same' is not the same thought over again, 243.

CHAPTER XV.

DISCRIMINATION                                                       244

Discrimination and association; definition of discrimination, 244.

Conditions which favor it, 245. The sensation of difference, 246.

Differences inferred, 248. The analysis of compound objects, 248. To be

easily singled out, a quality should already be separately known, 250.

Dissociation by varying concomitants, 251. Practice improves

discrimination, 252.

CHAPTER XVI.

ASSOCIATION                                                          253

The order of our ideas, 253. It is determined by cerebral laws, 255. The

ultimate cause of association is habit, 256. The elementary law in

association, 257. Indeterminateness of its results, 258. Total recall,

259. Partial recall, and the law of interest, 261. Frequency, recency,

vividness, and emotional congruity tend to determine the object

recalled, 264. Focalized recall, or 'association by similarity,' 267.

Voluntary trains of thought, 271. The solution of problems, 273.

Similarity no elementary law; summary and conclusion, 277.

CHAPTER XVII.

THE SENSE OF TIME                                                    280

The sensible present has duration, 280. We have no sense for absolutely

empty time, 281. We measure duration by the events which succeed in it,

283. The feeling of past time is a present feeling, 285. Due to a

constant cerebral condition, 286.

CHAPTER XVIII.

MEMORY                                                               287

What it is, 287. It involves both retention and recall, 289. Both

elements explained by paths formed by habit in the brain, 290. Two

conditions of a good memory, persistence and numerousness of paths,

292. Cramming, 295. One's native retentiveness is unchangeable, 296.

Improvement of the memory, 298. Recognition, 299. Forgetting, 300.

Pathological conditions, 301.

CHAPTER XIX.

IMAGINATION                                                          302

What it is, 302. Imaginations differ from man to man; Galton's

statistics of visual imagery, 303. Images of sounds, 306. Images of

movement, 307. Images of touch, 308. Loss of images in aphasia, 309. The

neural process in imagination, 310.

CHAPTER XX.

PERCEPTION                                                           312

Perception and sensation compared, 312. The perceptive state of mind is

not a compound, 313. Perception is of definite things, 316. Illusions,

317. First type: inference of the more usual object, 318. Second type:

inference of the object of which our mind is full, 321. 'Apperception,'

326. Genius and old-fogyism, 327. The physiological process in

perception, 329. Hallucinations, 330.

CHAPTER XXI.

THE PERCEPTION OF SPACE                                              335

The attribute of extensity belongs to all objects of sensation, 335. The

construction of real space, 337. The processes which it involves: 1)

Subdivision, 338; 2) Coalescence of different sensible data into one

'thing,' 339; 3) Location in an environment, 340; 4) Place in a series

of positions, 341; 5) Measurement, 342. Objects which are signs, and

objects which are realities, 345. The 'third dimension,' Berkeley's

theory of distance, 346. The part played by the intellect in

space-perception, 349.

CHAPTER XXII.

REASONING                                                            351

What it is, 351. It involves the use of abstract characters, 353. What

is meant by an 'essential' character, 354. The 'essence' varies with the

subjective interest, 358. The two great points in reasoning, 'sagacity'

and 'wisdom,' 360. Sagacity, 362. The help given by association by

similarity, 364. The reasoning powers of brutes, 367.

CHAPTER XXIII.

CONSCIOUSNESS AND MOVEMENT                                           370

All consciousness is motor, 370. Three classes of movement to which it

leads, 372.

CHAPTER XXIV.

EMOTION                                                              373

Emotions compared with instincts, 373. The varieties of emotion are

innumerable, 374. The cause of their varieties, 375. The feeling, in the

coarser emotions, results from the bodily expression, 375. This view

must not be called materialistic, 380. This view explains the great

variability of emotion, 381. A corollary verified, 382. An objection

replied to, 383. The subtler emotions, 384. Description of fear, 385.

Genesis of the emotional reactions, 386.

CHAPTER XXV.

INSTINCT                                                             391

Its definition, 391. Every instinct is an impulse, 392. Instincts are

not always blind or invariable, 395. Two principles of non-uniformity,

398. Enumeration of instincts in man, 406. Description of fear, 407.

CHAPTER XXVI.

WILL                                                                 415

Voluntary acts, 415. They are secondary performances, 415. No third kind

of idea is called for, 418. The motor-cue, 420. Ideo-motor action, 432.

Action after deliberation, 428. Five chief types of decision, 429. The

feeling of effort, 434. Healthiness of will, 435. Unhealthiness of will,

436. The explosive will: (1) from defective inhibition, 437; (2) from

exaggerated impulsion, 439. The obstructed will, 441. Effort feels like

an original force, 442. Pleasure and pain as springs of action, 444.

What holds attention determines action, 448. Will is a relation between

the mind and its 'ideas,' 449. Volitional effort is effort of

attention, 450. The question of free-will, 455. Ethical importance of

the phenomenon of effort, 458.

EPILOGUE.

PSYCHOLOGY AND PHILOSOPHY                                            461

What the word metaphysics means, 461. Relation of consciousness to the

brain, 462. The relation of states of mind to their 'objects,' 464. The

changing character of consciousness, 466. States of consciousness

themselves are not verifiable facts, 467.

PSYCHOLOGY.

CHAPTER I.

INTRODUCTORY.

=The definition of Psychology= may be best given in the words of Professor

Ladd, as the _description and explanation of states of consciousness as

such_. By states of consciousness are meant such things as sensations,

desires, emotions, cognitions, reasonings, decisions, volitions, and the

like. Their 'explanation' must of course include the study of their

causes, conditions, and immediate consequences, so far as these can be

ascertained.

requires a word of commentary. Most thinkers have a faith that at bottom

there is but one Science of all things, and that until all is known, no

one thing can be completely known. Such a science, if realized, would be

Philosophy. Meanwhile it is far from being realized; and instead of it,

we have a lot of beginnings of knowledge made in different places, and

kept separate from each other merely for practical convenience' sake,

until with later growth they may run into one body of Truth. These

provisional beginnings of learning we call 'the Sciences' in the plural.

In order not to be unwieldy, every such science has to stick to its own

arbitrarily-selected problems, and to ignore all others. Every science

thus accepts certain data unquestioningly, leaving it to the other parts

of Philosophy to scrutinize their significance and truth. All the

natural sciences, for example, in spite of the fact that farther

reflection leads to Idealism, assume that a world of matter exists

altogether independently of the perceiving mind. Mechanical Science

assumes this matter to have 'mass' and to exert 'force,' defining these

terms merely phenomenally, and not troubling itself about certain

unintelligibilities which they present on nearer reflection. Motion

similarly is assumed by mechanical science to exist independently of the

mind, in spite of the difficulties involved in the assumption. So

Physics assumes atoms, action at a distance, etc., uncritically;

Chemistry uncritically adopts all the data of Physics; and Physiology

adopts those of Chemistry. Psychology as a natural science deals with

things in the same partial and provisional way. In addition to the

'material world' with all its determinations, which the other sciences

of nature assume, she assumes additional data peculiarly her own, and

leaves it to more developed parts of Philosophy to test their ulterior

significance and truth. These data are--

1. _Thoughts and feelings_, or whatever other names transitory _states

of consciousness_ may be known by.

2. _Knowledge_, by these states of consciousness, of other things. These

things may be material objects and events, or other states of mind. The

material objects may be either near or distant in time and space, and

the states of mind may be those of other people, or of the thinker

himself at some other time.

How one thing _can_ know another is the problem of what is called the

Theory of Knowledge. How such a thing as a 'state of mind' can be at all

is the problem of what has been called Rational, as distinguished from

Empirical, Psychology. The _full_ truth about states of mind cannot be

known until both Theory of Knowledge and Rational Psychology have said

their say. Meanwhile an immense amount of provisional truth about them

can be got together, which will work in with the larger truth and be

interpreted by it when the proper time arrives. Such a provisional body

of propositions about states of mind, and about the cognitions which

they enjoy, is what I mean by Psychology considered as a natural

science. On any ulterior theory of matter, mind, and knowledge, the

facts and laws of Psychology thus understood will have their value. If

critics find that this natural-science point of view cuts things too

arbitrarily short, they must not blame the book which confines itself to

that point of view; rather must they go on themselves to complete it by

their deeper thought. Incomplete statements are often practically

necessary. To go beyond the usual 'scientific' assumptions in the

present case, would require, not a volume, but a shelfful of volumes,

and by the present author such a shelfful could not be written at all.

Let it also be added that =the human mind is all that can be touched upon=

in this book. Although the mental life of lower creatures has been

examined into of late years with some success, we have no space for its

consideration here, and can only allude to its manifestations

incidentally when they throw light upon our own.

=Mental facts cannot be properly studied apart from the physical

environment of which they take cognizance.= The great fault of the older

rational psychology was to set up the soul as an absolute spiritual

being with certain faculties of its own by which the several activities

of remembering, imagining, reasoning, willing, etc., were explained,

almost without reference to the peculiarities of the world with which

these activities deal. But the richer insight of modern days perceives

that our inner faculties are _adapted_ in advance to the features of the

world in which we dwell, adapted, I mean, so as to secure our safety and

prosperity in its midst. Not only are our capacities for forming new

habits, for remembering sequences, and for abstracting general

properties from things and associating their usual consequences with

them, exactly the faculties needed for steering us in this world of

mixed variety and uniformity, but our emotions and instincts are

adapted to very special features of that world. In the main, if a

phenomenon is important for our welfare, it interests and excites us the

first time we come into its presence. Dangerous things fill us with

involuntary fear; poisonous things with distaste; indispensable things

with appetite. Mind and world in short have been evolved together, and

in consequence are something of a mutual fit. The special interactions

between the outer order and the order of consciousness, by which this

harmony, such as it is, may in the course of time have come about, have

been made the subject of many evolutionary speculations, which, though

they cannot so far be said to be conclusive, have at least refreshed and

enriched the whole subject, and brought all sorts of new questions to

the light.

The chief result of all this more modern view is the gradually growing

conviction that =mental life is primarily teleological=; that is to say,

that our various ways of feeling and thinking have grown to be what they

are because of their utility in shaping our _reactions_ on the outer

world. On the whole, few recent formulas have done more service in

psychology than the Spencerian one that the essence of mental life and

bodily life are one, namely, 'the adjustment of inner to outer

relations.' The adjustment is to immediately present objects in lower

animals and in infants. It is to objects more and more remote in time

and space, and inferred by means of more and more complex and exact

processes of reasoning, when the grade of mental development grows more

advanced.

Primarily then, and fundamentally, the mental life is for the sake of

action of a preservative sort. Secondarily and incidentally it does many

other things, and may even, when ill 'adapted,' lead to its possessor's

destruction. Psychology, taken in the widest way, ought to study every

sort of mental activity, the useless and harmful sorts as well as that

which is 'adapted.' But the study of the harmful in mental life has been

made the subject of a special branch called 'Psychiatry'--the science of

insanity--and the study of the useless is made over to 'Æsthetics.'

Æsthetics and Psychiatry will receive no special notice in this book.

=All mental states= (no matter what their character as regards utility may

be) =are followed by bodily activity of some sort.= They lead to

inconspicuous changes in breathing, circulation, general muscular

tension, and glandular or other visceral activity, even if they do not

lead to conspicuous movements of the muscles of voluntary life. Not only

certain particular states of mind, then (such as those called volitions,

for example), but states of mind as such, _all_ states of mind, even

mere thoughts and feelings, are _motor_ in their consequences. This will

be made manifest in detail as our study advances. Meanwhile let it be

set down as one of the fundamental facts of the science with which we

are engaged.

It was said above that the 'conditions' of states of consciousness must

be studied. =The immediate condition of a state of consciousness is an

activity of some sort in the cerebral hemispheres.= This proposition is

supported by so many pathological facts, and laid by physiologists at

the base of so many of their reasonings, that to the medically educated

mind it seems almost axiomatic. It would be hard, however, to give any

short and peremptory proof of the unconditional dependence of mental

action upon neural change. That a general and usual amount of dependence

exists cannot possibly be ignored. One has only to consider how quickly

consciousness may be (so far as we know) abolished by a blow on the

head, by rapid loss of blood, by an epileptic discharge, by a full dose

of alcohol, opium, ether, or nitrous oxide--or how easily it may be

altered in quality by a smaller dose of any of these agents or of

others, or by a fever,--to see how at the mercy of bodily happenings our

spirit is. A little stoppage of the gall-duct, a swallow of cathartic

medicine, a cup of strong coffee at the proper moment, will entirely

overturn for the time a man's views of life. Our moods and resolutions

are more determined by the condition of our circulation than by our

logical grounds. Whether a man shall be a hero or a coward is a matter

of his temporary 'nerves.' In many kinds of insanity, though by no means

in all, distinct alterations of the brain-tissue have been found.

Destruction of certain definite portions of the cerebral hemispheres

involves losses of memory and of acquired motor faculty of quite

determinate sorts, to which we shall revert again under the title of

_aphasias_. Taking all such facts together, the simple and radical

conception dawns upon the mind that mental action may be uniformly and

absolutely a function of brain-action, varying as the latter varies, and

being to the brain-action as effect to cause.

'physiological psychology' of recent years=, and it will be the working

hypothesis of this book. Taken thus absolutely, it may possibly be too

sweeping a statement of what in reality is only a partial truth. But the

only way to make sure of its unsatisfactoriness is to apply it seriously

to every possible case that can turn up. To work an hypothesis 'for all

it is worth' is the real, and often the only, way to prove its

insufficiency. I shall therefore assume without scruple at the outset

that the uniform correlation of brain-states with mind-states is a law

of nature. The interpretation of the law in detail will best show where

its facilities and where its difficulties lie. To some readers such an

assumption will seem like the most unjustifiable _a priori_ materialism.

In one sense it doubtless is materialism: it puts the Higher at the

mercy of the Lower. But although we affirm that the _coming to pass_ of

thought is a consequence of mechanical laws,--for, according to another

'working hypothesis,' that namely of physiology, the laws of

brain-action are at bottom mechanical laws,--we do not in the least

explain the _nature_ of thought by affirming this dependence, and in

that latter sense our proposition is not materialism. The authors who

most unconditionally affirm the dependence of our thoughts on our brain

to be a fact are often the loudest to insist that the fact is

inexplicable, and that the intimate essence of consciousness can never

be rationally accounted for by any material cause. It will doubtless

take several generations of psychologists to test the hypothesis of

dependence with anything like minuteness. The books which postulate it

will be to some extent on conjectural ground. But the student will

remember that the Sciences constantly have to take these risks, and

habitually advance by zig--zagging from one absolute formula to another

which corrects it by going too far the other way. At present Psychology

is on the materialistic tack, and ought in the interests of ultimate

success to be allowed full headway even by those who are certain she

will never fetch the port without putting down the helm once more. The

only thing that is perfectly certain is that when taken up into the

total body of Philosophy, the formulas of Psychology will appear with a

very different meaning from that which they suggest so long as they are

studied from the point of view of an abstract and truncated 'natural

science,' however practically necessary and indispensable their study

from such a provisional point of view may be.

=The Divisions of Psychology.=--So far as possible, then, we are to study

states of consciousness in correlation with their probable neural

conditions. Now the nervous system is well understood to-day to be

nothing but a machine for receiving impressions and discharging

reactions preservative to the individual and his kind--so much of

physiology the reader will surely know. Anatomically, therefore, the

nervous system falls into three main divisions, comprising--

    1) The fibres which carry currents in;

    2) The organs of central redirection of them; and

    3) The fibres which carry them out.

Functionally, we have sensation, central reflection, and motion, to

correspond to these anatomical divisions. In Psychology we may divide

our work according to a similar scheme, and treat successively of three

fundamental conscious processes and their conditions. The first will be

Sensation; the second will be Cerebration or Intellection; the third

will be the Tendency to Action. Much vagueness results from this

division, but it has practical conveniences for such a book as this, and

they may be allowed to prevail over whatever objections may be urged.

CHAPTER II.

SENSATION IN GENERAL.

brain.= The human nerve-centres are surrounded by many dense wrappings of

which the effect is to protect them from the direct action of the forces

of the outer world. The hair, the thick skin of the scalp, the skull,

and two membranes at least, one of them a tough one, surround the brain;

and this organ moreover, like the spinal cord, is bathed by a serous

fluid in which it floats suspended. Under these circumstances the only

things that can _happen_ to the brain are:

1) The dullest and feeblest mechanical jars;

2) Changes in the quantity and quality of the blood-supply; and

3) Currents running in through the so-called afferent or centripetal

nerves.

The mechanical jars are usually ineffective; the effects of the

blood-changes are usually transient; the nerve-currents, on the

contrary, produce consequences of the most vital sort, both at the

moment of their arrival, and later, through the invisible paths of

escape which they plough in the substance of the organ and which, as we

believe, remain as more or less permanent features of its structure,

modifying its action throughout all future time.

is played upon and excited to its inward activity by a particular force

of the outer world.= Usually it is insensible to other forces: thus the

optic nerves are not impressible by air-waves, nor those of the skin by

light-waves. The lingual nerve is not excited by aromatic effluvia, the

auditory nerve is unaffected by heat. Each selects from the vibrations

of the outer world some one rate to which it responds exclusively. The

result is that our sensations form a discontinuous series, broken by

enormous gaps. There is no reason to suppose that the order of

vibrations in the outer world is anything like as interrupted as the

order of our sensations. Between the quickest audible air-waves (40,000

vibrations a second at the outside) and the slowest sensible heat-waves

(which number probably billions), Nature must somewhere have realized

innumerable intermediary rates which we have no nerves for perceiving.

The process in the nerve-fibres themselves is very likely the same, or

much the same, in all the different nerves. It is the so-called

'current'; but the current is _started_ by one order of outer vibrations

in the retina, and in the ear, for example, by another. This is due to

the different _terminal organs_ with which the several afferent nerves

are armed. Just as we arm ourselves with a spoon to pick up soup, and

with a fork to pick up meat, so our nerve-fibres arm themselves with one

sort of end-apparatus to pick up air-waves, with another to pick up

ether-waves. The terminal apparatus always consists of modified

epithelial cells with which the fibre is continuous. The fibre itself is

not directly excitable by the outer agent which impresses the terminal

organ. The optic fibres are unmoved by the direct rays of the sun; a

cutaneous nerve-trunk may be touched with ice without feeling cold.[2]

The fibres are mere transmitters; the terminal organs are so many

imperfect telephones into which the material world speaks, and each of

which takes up but a portion of what it says; the brain-cells at the

fibres' central end are as many others at which the mind listens to the

far-off call.

=The 'Specific Energies' of the Various Parts of the Brain.=--To a certain

extent anatomists have traced definitely the paths which the sensory

nerve-fibres follow after their entrance into the centres, as far as

their termination in the gray matter of the cerebral convolutions.[3] It

will be shown on a later page that the consciousness which accompanies

the excitement of this gray matter varies from one portion of it to

another. It is consciousness of things seen, when the occipital lobes,

and of things heard, when the upper part of the temporal lobes, share in

the excitement. Each region of the cerebral cortex responds to the

stimulation which its afferent fibres bring to it, in a manner with

which a peculiar quality of feeling seems invariably correlated. This is

what has been called the law of 'specific energies' in the nervous

system. Of course we are without even a conjectural explanation of the

_ground_ of such a law. Psychologists (as Lewes, Wundt, Rosenthal,

Goldscheider, etc.) have debated a good deal as to whether the specific

quality of the feeling depends solely on the _place_ stimulated in the

cortex, or on the _sort of current_ which the nerve pours in. Doubtless

the sort of outer force habitually impinging on the end-organ gradually

modifies the end-organ, the sort of commotion received from the

end-organ modifies the fibre, and the sort of current a so-modified

fibre pours into the cortical centre modifies the centre. The

modification of the centre in turn (though no man can guess how or why)

seems to modify the resultant consciousness. But these adaptive

modifications must be excessively slow; and as matters actually stand in

any adult individual, it is safe to say that, more than anything else,

the _place_ excited in his cortex decides what kind of thing he shall

feel. Whether we press the retina, or prick, cut, pinch, or galvanize

the living optic nerve, the Subject always feels flashes of light, since

the ultimate result of our operations is to stimulate the cortex of his

occipital region. Our habitual ways of feeling outer things thus depend

on which convolutions happen to be connected with the particular

end-organs which those things impress. We _see_ the sunshine and the

fire, simply because the only peripheral end-organ susceptible of taking

up the ether-waves which these objects radiate excites those particular

fibres which run to the centres of sight. If we could interchange the

inward connections, we should feel the world in altogether new ways. If,

for instance, we could splice the outer extremity of our optic nerves to

our ears, and that of our auditory nerves to our eyes, we should hear

the lightning and see the thunder, see the symphony and hear the

conductor's movements. Such hypotheses as these form a good training for

neophytes in the idealistic philosophy!

=Sensation distinguished from Perception.=--It is impossible rigorously to

_define_ a sensation; and in the actual life of consciousness

sensations, popularly so called, and perceptions merge into each other

by insensible degrees. All we can say is that _what we mean by

sensations are_ FIRST _things in the way of consciousness_. They are the

_immediate_ results upon consciousness of nerve-currents as they enter

the brain, and before they have awakened any suggestions or associations

with past experience. But it is obvious that _such immediate sensations

can only be realized in the earliest days of life_. They are all but

impossible to adults with memories and stores of associations acquired.

Prior to all impressions on sense-organs, the brain is plunged in deep

sleep and consciousness is practically non-existent. Even the first

weeks after birth are passed in almost unbroken sleep by human infants.

It takes a strong message from the sense-organs to break this slumber.

In a new-born brain this gives rise to an absolutely pure sensation. But

the experience leaves its 'unimaginable touch' on the matter of the

convolutions, and the next impression which a sense-organ transmits

produces a cerebral reaction in which the awakened vestige of the last

impression plays its part. Another sort of feeling and a higher grade of

cognition are the consequence. 'Ideas' _about_ the object mingle with

the awareness of its mere sensible presence, we name it, class it,

compare it, utter propositions concerning it, and the complication of

the possible consciousness which an incoming current may arouse, goes on

increasing to the end of life. In general, this higher consciousness

about things is called Perception, the mere inarticulate feeling of

their presence is Sensation, so far as we have it at all. To some degree

we seem able to lapse into this inarticulate feeling at moments when our

attention is entirely dispersed.

=Sensations are cognitive.= A sensation is thus an abstraction seldom

realized by itself; and the object which a sensation knows is an

abstract object which cannot exist alone. _'Sensible qualities' are the

objects of sensation._ The sensations of the eye are aware of the

_colors_ of things, those of the ear are acquainted with their _sounds_;

those of the skin feel their tangible _heaviness_, _sharpness_, _warmth_

or _coldness_, etc., etc. From all the organs of the body currents may

come which reveal to us the quality of _pain_, and to a certain extent

that of _pleasure_.

Such qualities as _stickiness_, _roughness_, etc., are supposed to be

felt through the coöperation of muscular sensations with those of the

skin. The geometrical qualities of things, on the other hand, their

_shapes_, _bignesses_, _distances_, etc. (so far as we discriminate and

identify them), are by most psychologists supposed to be impossible

without the evocation of memories from the past; and the cognition of

these attributes is thus considered to exceed the power of sensation

pure and simple.

='Knowledge of Acquaintance' and 'Knowledge about.'=--Sensation, thus

considered, differs from perception only in the extreme simplicity of

its object or content. Its object, being a simple quality, is sensibly

_homogeneous_; and its function is that of mere _acquaintance_ with this

homogeneous seeming fact. Perception's function, on the other hand, is

that of knowing something _about_ the fact. But we must know _what_ fact

we mean, all the while, and the various _whats_ are what sensations

give. Our earliest thoughts are almost exclusively sensational. They

give us a set of _whats_, or _thats_, or _its_; of subjects of discourse

in other words, with their relations not yet brought out. The first time

we see _light_, in Condillac's phrase we _are_ it rather than see it.

But all our later optical knowledge is about what this experience gives.

And though we were struck blind from that first moment, our scholarship

in the subject would lack no essential feature so long as our memory

remained. In training-institutions for the blind they teach the pupils

as much _about_ light as in ordinary schools. Reflection, refraction,

the spectrum, the ether-theory, etc., are all studied. But the best

taught born-blind pupil of such an establishment yet lacks a knowledge

which the least instructed seeing baby has. They can never show him

_what_ light is in its 'first intention'; and the loss of that sensible

knowledge no book-learning can replace. All this is so obvious that we

usually find sensation 'postulated' as an element of experience, even by

those philosophers who are least inclined to make much of its

importance, or to pay respect to the knowledge which it brings.

=Sensations distinguished from Images.=--Both sensation and perception,

for all their difference, are yet alike in that their objects appear

_vivid_, _lively_, and _present_. Objects merely _thought of_,

_recollected_, or _imagined_, on the contrary, are relatively faint and

devoid of this pungency, or tang, this quality of _real presence_ which

the objects of sensation possess. Now the cortical brain-processes to

which sensations are attached are due to incoming currents from the

periphery of the body--an external object must excite the eye, ear,

etc., before the sensation comes. Those cortical processes, on the other

hand, to which mere ideas or images are attached are due in all

probability to currents from other convolutions. It would seem, then,

that the currents from the periphery normally awaken a kind of

brain-activity which the currents from other convolutions are inadequate

to arouse. To this sort of activity--a profounder degree of

disintegration, perhaps--the quality of vividness, presence, or reality

in the object of the resultant consciousness seems correlated.

=The Exteriority of Objects of Sensation.=--Every thing or quality felt is

felt in outer space. It is impossible to conceive a brightness or a

color otherwise than as extended and outside of the body. Sounds also

appear in space. Contacts are against the body's surface; and pains

always occupy some organ. An opinion which has had much currency in

psychology is that sensible qualities are first apprehended as _in the

mind itself_, and then 'projected' from it, or 'extradited,' by a

secondary intellectual or super-sensational mental act. There is no

ground whatever for this opinion. The only facts which even seem to make

for it can be much better explained in another way, as we shall see

later on. The very first sensation which an infant gets _is_ for him the

outer universe. And the universe which he comes to know in later life is

nothing but an amplification of that first simple germ which, by

accretion on the one hand and intussusception on the other, has grown so

big and complex and articulate that its first estate is unrememberable.

In his dumb awakening to the consciousness of _something there_, a mere

_this_ as yet (or something for which even the term _this_ would perhaps

be too discriminative, and the intellectual acknowledgment of which

would be better expressed by the bare interjection 'lo!'), the infant

encounters an object in which (though it be given in a pure sensation)

all the 'categories of the understanding' are contained. _It has

externality, objectivity, unity, substantiality, causality, in the full

sense in which any later object or system of objects has these things._

Here the young knower meets and greets his world; and the miracle of

knowledge bursts forth, as Voltaire says, as much in the infant's lowest

sensation as in the highest achievement of a Newton's brain.

The physiological condition of this first sensible experience is

probably many nerve-currents coming in from various peripheral organs at

once; but this multitude of organic conditions does not prevent the

consciousness from being one consciousness. We shall see as we go on

that it can be one consciousness, even though it be due to the

coöperation of numerous organs and be a consciousness of many things

together. The Object which the numerous inpouring currents of the baby

bring to his consciousness is one big blooming buzzing Confusion. That

Confusion is the baby's universe; and the universe of all of us is still

to a great extent such a Confusion, potentially resolvable, and

demanding to be resolved, but not yet actually resolved, into parts. It

appears from first to last as a space-occupying thing. So far as it is

unanalyzed and unresolved we may be said to know it sensationally; but

as fast as parts are distinguished in it and we become aware of their

relations, our knowledge becomes perceptual or even conceptual, and as

such need not concern us in the present chapter.

=The Intensity of Sensations.=--A light may be so weak as not sensibly to

dispel the darkness, a sound so low as not to be heard, a contact so

faint that we fail to notice it. In other words, a certain finite amount

of the outward stimulus is required to produce any sensation of its

presence at all. This is called by Fechner the law of the

_threshold_--something must be stepped over before the object can gain

entrance to the mind. An impression just above the threshold is called

the _minimum visibile_, _audibile_, etc. From this point onwards, as

the impressing force increases, the sensation increases also, though at

a slower rate, until at last an _acme_ of the sensation is reached which

no increase in the stimulus can make sensibly more great. Usually,

before the acme, _pain_ begins to mix with the specific character of the

sensation. This is definitely observable in the cases of great pressure,

intense heat, cold, light, and sound; and in those of smell and taste

less definitely so only from the fact that we can less easily increase

the force of the stimuli here. On the other hand, all sensations,

however unpleasant when more intense, are rather agreeable than

otherwise in their very lowest degrees. A faintly bitter taste, or

putrid smell, may at least be _interesting_.

[Illustration: FIG. 1.]

=Weber's Law.=--I said that the intensity of the sensation increases by

slower steps than those by which its exciting cause increases. If there

were no threshold, and if every equal increment in the outer stimulus

produced an equal increment in the sensation's intensity, a simple

straight line would represent graphically the 'curve' of the relation

between the two things. Let the horizontal line stand for the scale of

intensities of the objective stimulus, so that at 0 it has no intensity,

at 1 intensity 1, and so forth. Let the verticals dropped from the

slanting line stand for the sensations aroused. At 0 there will be no

sensation; at 1 there will be a sensation represented by the length of

the vertical _S_¹--1, at 2 the sensation will be represented by

_S_²--2, and so on. The line of _S_'s will rise evenly because by the

hypothesis the verticals (or sensations) increase at the same rate as

the horizontals (or stimuli) to which they severally correspond. But in

Nature, as aforesaid, they increase at a slower rate. If each step

forward in the horizontal direction be equal to the last, then each step

upward in the vertical direction will have to be somewhat shorter than

the last; the line of sensations will be convex on top instead of

straight.

[Illustration: FIG. 2.]

Fig. 2 represents this actual state of things, 0 being the zero-point of

the stimulus, and conscious sensation, represented by the curved line,

not beginning until the 'threshold' is reached, at which the stimulus

has the value 3. From here onwards the sensation increases, but it

increases less at each step, until at last, the 'acme' being reached,

the sensation-line grows flat. The exact law of retardation is called

_Weber's law_, from the fact that he first observed it in the case of

weights. I will quote Wundt's account of the law and of the facts on

which it is based.

     "Every one knows that in the stilly night we hear things unnoticed

     in the noise of day. The gentle ticking of the clock, the air

     circulating through the chimney, the cracking of the chairs in the

     room, and a thousand other slight noises, impress themselves upon

     our ear. It is equally well known that in the confused hubbub of

     the streets, or the clamor of a railway, we may lose not only what

     our neighbor says to us, but even not hear the sound of our own

     voice. The stars which are brightest at night are invisible by

     day; and although we see the moon then, she is far paler than at

     night. Every one who has had to deal with weights knows that if to

     a pound in the hand a second pound be added, the difference is

     immediately felt; whilst if it be added to a hundredweight, we are

     not aware of the difference at all....

     "The sound of the clock, the light of the stars, the pressure of

     the pound, these are all _stimuli_ to our senses, and stimuli whose

     outward amount remains the same. What then do these experiences

     teach? Evidently nothing but this, that one and the same stimulus,

     according to the circumstances under which it operates, will be

     felt either more or less intensely, or not felt at all. Of what

     sort now is the alteration in the circumstances upon which this

     alteration in the feeling may depend? On considering the matter

     closely we see that it is everywhere of one and the same kind. The

     tick of the clock is a feeble stimulus for our auditory nerve,

     which we hear plainly when it is alone, but not when it is added to

     the strong stimulus of the carriage-wheels and other noises of the

     day. The light of the stars is a stimulus to the eye. But if the

     stimulation which this light exerts be added to the strong stimulus

     of daylight, we feel nothing of it, although we feel it distinctly

     when it unites itself with the feebler stimulation of the twilight.

     The poundweight is a stimulus to our skin, which we feel when it

     joins itself to a preceding stimulus of equal strength, but which

     vanishes when it is combined with a stimulus a thousand times

     greater in amount.

     "We may therefore lay it down as a general rule that a stimulus, in

     order to be felt, may be so much the smaller if the already

     preëxisting stimulation of the organ is small, but must be so much

     the larger, the greater the preëxisting stimulation is.... The

     simplest relation would obviously be that the sensation should

     increase in identically the same ratio as the stimulus.... But if

     this simplest of all relations prevailed, ... the light of the

     stars, e.g., ought to make as great an addition to the daylight as

     it does to the darkness of the nocturnal sky, and this we know to

     be not the case.... So it is clear that the strength of the

     sensations does not increase in proportion to the amount of the

     stimuli, but more slowly. And now comes the question, in what

     proportion does the increase of the sensation grow less as the

     increase of the stimulus grows greater? To answer this question,

     every-day experiences do not suffice. We need exact measurements,

     both of the amounts of the various stimuli, and of the intensity of

     the sensations themselves.

     "How to execute these measurements, however, is something which

     daily experience suggests. To measure the strength of sensations

     is, as we saw, impossible; we can only measure the difference of

     sensations. Experience showed us what very unequal differences of

     sensation might come from equal differences of outward stimulus.

     But all these experiences expressed themselves in one kind of fact,

     that the same difference of stimulus could in one case be felt, and

     in another case not felt at all--a pound felt if added to another

     pound, but not if added to a hundredweight.... We can quickest

     reach a result with our observations if we start with an arbitrary

     strength of stimulus, notice what sensation it gives us, and then

     _see how much we can increase the stimulus without making the

     sensation seem to change_. If we carry out such observations with

     stimuli of varying absolute amounts, we shall be forced to choose

     in an equally varying way the amounts of addition to the stimulus

     which are capable of giving us a just barely perceptible feeling of

     _more_. A light to be just perceptible in the twilight need not be

     near as bright as the starlight; it must be far brighter to be just

     perceived during the day. If now we institute such observations for

     all possible strengths of the various stimuli, and note for each

     strength the amount of addition of the latter required to produce a

     barely perceptible alteration of sensation, we shall have a series

     of figures in which is immediately expressed the law according to

     which the sensation alters when the stimulation is increased...."

Observations according to this method are particularly easy to make in

the spheres of light, sound, and pressure. Beginning with the latter

case,

     "We find a surprisingly simple result. _The barely sensible

     addition to the original weight must stand exactly in the same

     proportion to it_, be the _same fraction_ of it, no matter what the

     absolute value may be of the weights on which the experiment is

     made.... As the average of a number of experiments, this fraction

     is found to be about ⅓; that is, no matter what pressure there may

     already be made upon the skin, an increase or a diminution of the

     pressure will be _felt_, as soon as the added or subtracted weight

     amounts to one third of the weight originally there."

Wundt then describes how differences may be observed in the muscular

feelings, in the feelings of heat, in those of light, and in those of

sound; and he concludes thus:

     "So we have found that all the senses whose stimuli we are enabled

     to measure accurately, obey a uniform law. However various may be

     their several delicacies of discrimination, _this_ holds true of

     all, that _the increase of the stimulus necessary to produce an

     increase of the sensation bears a constant ratio to the total

     stimulus_. The figures which express this ratio in the several

     senses may be shown thus in tabular form:

    Sensation of light          1/100

    Muscular sensation          1/17

    Feeling of pressure, }

       "    "  warmth,   }      1/3

       "    "  sound,    }

     "These figures are far from giving as accurate a measure as might

     be desired. But at least they are fit to convey a general notion of

     the relative discriminative susceptibility of the different

     senses.... The important law which gives in so simple a form the

     relation of the sensation to the stimulus that calls it forth was

     first discovered by the physiologist Ernst Heinrich Weber to obtain

     in special cases."[4]

=Fechner's Law.=--Another way of expressing Weber's law is to say that to

get equal positive additions to the sensation, one must make equal

_relative_ additions to the stimulus. Professor Fechner of Leipzig

founded upon Weber's law a theory of the numerical measurement of

sensations, over which much metaphysical discussion has raged. Each just

perceptible addition to the sensation, as we gradually let the stimulus

increase, was supposed by him to be a _unit_ of sensation, and all these

units were treated by him as equal, in spite of the fact that _equally

perceptible_ increments need by no means appear _equally big_ when they

once are perceived. The many pounds which form the just perceptible

addition to a hundredweight feel bigger when added than the few ounces

which form the just perceptible addition to a pound. Fechner ignored

this fact. He considered that if _n_ distinct perceptible steps of

increase might be passed through in gradually increasing a stimulus from

the threshold-value till the intensity _s_ was felt, then the sensation

of _s_ was composed of _n_ units, which were of the same value all along

the line.[5] Sensations once represented by numbers, psychology may

become, according to Fechner, an 'exact' science, susceptible of

mathematical treatment. His general formula for getting at the number of

sensation, _R_ for the stimulus numerically estimated, and _C_ for a

constant that must be separately determined by experiment in each

particular order of sensibility. The sensation is proportional to the

logarithm of the stimulus; and the absolute values, in units, of any

series of sensations might be got from the ordinates of the curve in

Fig. 2, if it were a correctly drawn logarithmic curve, with the

thresholds rightly plotted out from experiments.

Fechner's psycho-physic formula, as he called it, has been attacked on

every hand; and as absolutely nothing practical has come of it, it need

receive no farther notice here. The main outcome of his book has been to

stir up experimental investigation into the validity of Weber's law

(which concerns itself merely with the just perceptible increase, and

says nothing about the measurement of the sensation as a whole) and to

promote discussion of statistical methods. Weber's law, as will appear

when we take the senses, _seriatim_, is only approximately verified. The

discussion of statistical methods is necessitated by the extraordinary

fluctuations of our sensibility from one moment to the next. It is

found, namely, when the difference of two sensations approaches the

limit of discernibility, that at one moment we discern it and at the

next we do not. Our incessant accidental inner alterations make it

impossible to tell just what the least discernible increment of the

sensation is without taking the average of a large number of

appreciations. These _accidental errors_ are as likely to increase as to

diminish our sensibility, and are eliminated in such an average, for

those above and those below the line then neutralize each other in the

sum, and the normal sensibility, if there be one (that is, the

sensibility due to constant causes as distinguished from these

accidental ones), stands revealed. The methods of getting the average

all have their difficulties and their snares, and controversy over them

has become very subtle indeed. As an instance of how laborious some of

the statistical methods are, and how patient German investigators can

be, I may say that Fechner himself, in testing Weber's law for weights

by the so-called 'method of true and false cases,' tabulated and

computed no less than 24,576 separate judgments.

=Sensations are not compounds.= The fundamental objection to Fechner's

whole attempt seems to be this, that although the outer _causes_ of our