CHAPTER IV.

THE CLASSIFICATION AND THE NOMENCLATURE OF MENTAL OPERATIONS.

IF, as has been set forth in the preceding chapter, all mental states are effects of physical causes, it follows that what are called mental faculties and operations are, properly speaking, cerebral functions, allotted to definite, though not yet precisely assignable, parts of the brain.

These functions appear to be reducible to three groups, namely Sensation, Correlation, and Ideation.

The organs of the functions of sensation and correlation are those portions of the cerebral substance, the molecular changes of which give rise to impressions of sensation and impressions of relation.

The changes in the nervous matter which bring about the effects which we call its functions, follow upon some kind of stimulus, and rapidly reaching their maximum, as rapidly die away. The effect of the irritation of a

nerve-fibre on the cerebral substance with which it is connected may be compared to the pulling of a long bell-wire. The impulse takes a little time to reach the bell; the bell rings and then becomes quiescent, until

acher pull is given. Sa in the brain every sensation the ring of a servirà partici, the effect of a nementary inpuist sem slang & nerve-libre,

there were a ranquese Ekeness between the two terns of this very rough and ready comparison, it is exus that there could be at such thing as memory. A del maris ne snähit sign of having been rung five minuses sga, soād the activity of a sensigenous cerebral particis might smisly leave no trace. Under these eirvumsðanos, agian, it would seem that the only impressions of relation which could arise would be those of evexistence and of similarity. For succession implies memory of an antecedent state

But the special pornlisrity of the cerebral apparatus is, that any given function which has once been performed is very assily set a gang again by causes more or loss different from those to which it owed its origin. Of the mechanism of this generation of images of impravedons or ideas in Hume's sense, which may be formed ideation, we know nothing at present, though This fast and its molts are fam.ise enough.

During our waking, and mary of our sleeping, hours, In fact, the fumetion of idostion is in continual, if not confimmons, activity. Tesins of thought, as we call Hum, smed one another without intermission, even den the starting of new trains by fresh sense-impresFarhana far as possible prevented. The rapidity and H: hub nalty of this idestions process are obviously 4 probent upon physiological conditions The widest

↑ Wath while, for the present purpose, to consider all myvioms, action, occupies a sensible time, the duraImpo don might not overlap that of the inpression # in the vase supposed.

differences in these resperse are constitutional in men of different temperamente: and are obervable in ce self, under varying one dries of hunger and repletion, fatigue and freshness, olines and entical exte ment. The minence of der in drane; of stimulantS upon the fulness and the velocity of the stream of thought; the delirious phantasma generated by disease, by hashish, or by alochel; will occur to every one as examples of the marvellous sensitiveness of the apparatus of ideation to parely physical inferoes

The succession of mental states in ideation is not fortuitous, but fellows the law of association, which may be stated thus: that every idea tends to be followed by some other idea which is associated with the first, or its impression, by a relation of succession, of contiguity, or of likeness.

Thus the idea of the word horse just now presented itself to my mind, and was followed in quick succession by the ideas of four legs, hoofs, teeth, rider, saddle, racing, cheating; all of which ideas are connected in my experience with the impression, or the idea, of a horse and with one another, by the relations of contiguity and succession. No great attention to what passes in the mind is needful to prove that our trains of thought are neither to be arrested, nor even permanently controlled, by our desires or emotions. Nevertheless they are largely influenced by them. In the presence of a strong desire, or emotion, the stream of thought no longer flows on in a straight course, but seems, as it were, to eddy round the idea of that which is the object of the emotion. Every one who has "eaten his bread in sorrow' knows how strangely the current of ideas whirls about the conception of the object of regret or

remorse as a centre; every now and then, indeed, breaking away into the new tracks suggested by passing associations, but still returning to the central thought. Few can have been so happy as to have escaped the social bore, whose pet notion is certain to crop up whatever topic is started; while the fixed idea of the monomaniac is but the extreme form of the same phenomenon. And as, on the one hand, it is so hard to drive away the thought we would fain be rid of; so, upon the other, the pleasant imaginations which we would so gladly retain are, sooner or later, jostled away by the crowd of claimants for birth into the world of consciousness; which hover as a sort of psychical possibilities, or inverse ghosts, the bodily presentments of spiritual phenomena to be, in the limbo of the brain. In that form of desire which is called "attention," the train of thought, held fast, for a time, in the desired direction, seems ever striving to get on to another line-and the junctions and sidings are so multitudinous !

The constituents of trains of ideas may be grouped in various ways.

Hume says:

"We find, by experience, that when any impression has been present in the mind, it again makes its appearance there as an idea, and this it may do in two different ways: either when, on its new appearance, it retains a considerable degree of its first vivacity, and is somewhat intermediate between an impression and an idea; or when it entirely loses that vivacity, and is a perfect idea. The faculty by which we repeat our impressions in the first manner, is called the memory, and the other the imagination.”—(I. pp. 23, 24.)

And he considers that the only difference between ideas of imagination and those of memory, except the

superior vivacity of the latter, lies in the fact that those of memory preserve the original order of the impressions from which they are derived, while the imagination "is free to transpose and change its ideas."

The latter statement of the difference between memory and imagination is less open to cavil than the former, though by no means unassailable.

The special characteristic of a memory surely is not its vividness; but that it is a complex idea, in which the idea of that which is remembered is related by co-existence with other ideas, and by antecedence with present impressions.

If I say I remember A. B., the chance acquaintance of ten years ago, it is not because my idea of A. B. is very vivid on the contrary, it is extremely faint-but because that idea is associated with ideas of impressions co-existent with those which I call A. B.; and that all these are at the end of the long series of ideas, which represent that much past time. In truth I have a much more vivid idea of Mr. Pickwick, or of Colonel Newcome, than I have of A. B.; but, associated with the ideas of these persons, I have no idea of their having ever been derived from the world of impressions; and so they are relegated to the world of imagination. On the other hand, the characteristic of an imagination may properly be said to lie not in its intensity, but in the fact that, as Hume puts it, "the arrangement," or the relations, of the ideas are different from those in which the impressions, whence these ideas are derived, occurred; or in other words, that the thing imagined has not happened. In popular usage, however, imagination is frequently employed for simple memory-" In imagination I was back in the old times."