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ness, or art. We occasionally meet with characters of this description; the famous admirable Crichton,' as usually described, is an example of the highest order of the class.

In the second place, I may advert to the known superiority of early years as regards this force or plasticity. It is impossible to state with any precision the comparative intensity of the adhesive growth at different ages, but there can be no doubt of the fact of its gradual diminution from infancy to old age. Bodily acquisitions are easiest while the organs are still flexible, apart from the plastic adhesiveness of the brain; hence a maximum age is fixed for receiving recruits in the military service. At the present time, I believe the age of twenty-three is the extreme term of admission. Up to this age any bodily habit is easily assumed; the moral discipline of obedience is also comparatively easy. But for both the one and the other the earliest years are the best. We must always take account of the obstruction arising from adverse bents and acquisitions. In matters where the bodily and mental system are not in any way pre-occupied, the age of twenty-five is a very plastic age, as, for example, in learning business forms, languages, or science. On the other hand, the voluntary command of the attention is greatest in mature life, a circumstance very much in favour of acquisition.

I remark finally that there is a temporary adhesiveness as distinguished from what is enduring or permanent. I can convey a lengthy message from one room to another, but am unable to reproduce it next day. The endurance of the first impression, while the mind is wholly occupied with it, is no surety for its being retained for a week or a month to come.

The illustration in this chapter has been mainly directed upon the enduring acquisitions. We have generally understood the retainability of an impression to mean the power of recalling it at any future time, however remote. But it is necessary to take account of the tendency of all acquisitions to decay by time; the rate of decay being dependent on various circumstances, and chiefly on the decay of the brain itself. It is observed that in old age the impressions that survive longest are those of early years.

G G

To keep our acquisitions from decaying it is requisite that they should be occasionally revived. A language acquired in early years may be utterly lost by disuse; if kept up till mature age it will be fixed for life. Sustained practice seems particularly necessary in early education: children's acquisitions are very liable to decompose if not kept up and confirmed by new additions. No precise laws have ever been ascertained in this department of the human mind.

The system of cramming is a scheme for making temporary acquisitions, regardless of the endurance of them. Excitable brains, that can command a very great concentration of force upon a subject, will be proportionably impressed for the time being. By drawing upon the strength of the future, we are able to fix temporarily a great variety of impressions during the exaltation of cerebral power that the excitement gives. The occasion past, the brain must lie idle for a corresponding length of time, while a large portion of the excited impressions will gradually perish away. This system is extremely unfavourable to permanent acquisitions; for these, the force of the brain should be carefully husbanded and temperately drawn upon. Every period of undue excitement and feverish susceptibility is a time of great waste of the plastic energy of the mind on the whole.

CHAPTER II.

I.

LAW OF SIMILARITY.

Present Actions, Sensations, Thoughts, or Emotions tend to revive their LIKE among previous Impressions.

CONT

ONTIGUITY joins together things that are naturally juxtaposed, or that are, by any circumstance, presented to the mind at the same time, as when we associate heat with light, a falling body with a concussion. But in addition to this link of reproductive connexion, we find that one thing will, by virtue of similarity, recal another separated from it in time; thus, if I see Lear acted to-day, I am put in mind of a former occasion, when I have seen the same play acted.

This tendency to be reminded of past occurrences and thoughts of every kind, through their resemblance to something present, is here termed the Law or Principle of Similarity. It is styled by Sir William Hamilton the Law of Repetition. He shows it to have been first recognised and enunciated by Aristotle.* But its application to explain particular phenomena has been gradually extended by many successive writers down to the present time.

2. Some preliminary explanation of the kind of relation subsisting between the two principles of Contiguity and Similarity is requisite in order to guard against mistakes, and especially to prevent a too easy misapprehension as to the radical distinctness of the two modes of action in the mental framework. When the cohesive link between any two contiguous actions or images is confirmed by a new occurrence or repetition, it is perfectly obvious that the present impression

* Dissertations on Reid, p. 889.

must revive the sum total of the past impressions, or reinstate the whole mental condition left on the occasion immediately preceding. Thus, if I am disciplining myself in the act of drawing a round figure with my hand, any one present effort must recal the state of the muscular and nervous action, or the precise bent acquired at the end of the previous effort, while that effort had to reinstate the condition attained at the end of the one preceding, and so on. It is only in this way that repetition can be of any avail in confirming a physical habit or forming an intellectual aggregate. But this reinstatement of a former condition by a present act of the same kind, is really and truly a case of the operation of the associating principle of similarity, or of like recalling like; and we here plainly see, that without such recal, the adhesion of contiguous things would be impossible. It would appear, therefore, that all through the exposition of Contiguity, the principle of Similarity has been tacitly assumed; we have always taken for granted, that the recurrence of any object to the view recalled the total impression made by all the previous occurrences, and added its own effect to that total. In a word, no one ever doubts the perfect operation of the principle of like recalling like, in any of the numerous instances above adduced as showing the growth of contiguous adhesion.

But by this tacit assumption of the unfailing operation of the force of anything present to reinstate the past impressions of the same thing, we restrict ourselves to those cases where the reinstatement is sure and certain, in fact to cases of absolute identity of the present and past. Such is the nature of the instances dwelt upon in the previous chapter: in all of them the new action, or the new image, was supposed precisely identical with the old, and went simply to reinstate and deepen an impression already made. We must, however, now pass beyond this class of examples and enter upon cases of a new description, where the identity is only partial, and is on that account liable to be missed; where the restoration, instead of being sure, is doubtful; and where, moreover, the reinstatement serves higher purposes than the mere iteration and

SIMILARITY INVOLVED IN CONTIGUITY.

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deepening of an impression already made. In all mental restorations whatsoever, both Contiguity and Similarity are at work; in one class the question is, as to the sufficiency of the contiguous bond, the similarity being sure; in another class the question is, as to the sufficiency of the attractive force of the likeness, the contiguous adhesiveness being believed secure. If I chance to meet with a person I have formerly seen, and endeavour to remember his name, it will depend upon the goodness of a cohesive link whether or not I succeed; there will be no difficulty in my recalling the past impression of his personal appearance through the force of the present impression; but having recalled the full total of the past impressions, I may not be able to recover the accompaniment of the name; the contiguity may be at fault, although the similarity works its perfect work of restoring me to my previous conception of the personal aspect. If, on the other hand, I see a man on the street, and if I have formerly seen a portrait of that man, it is a question whether the living reality shall recal the portrait; the doubt hangs not upon the contiguity, or coherence of the parts of the picture, if it could be recalled, but upon the chance of its being recalled at all. Where things are identical, the operation of similarity in making the present case revive the former ones is so certain, that it is not even mentioned; we talk of the goodness of the cohesive bond between the revived part and its accompaniments, as if contiguity expressed the whole fact of the restoration. To make up for this partiality of view, which was indispensable to a clear exposition, we now embrace with the same partial and prominent consideration the element that was left in a tacit condition, and allow to sink into the same tacit state the one that has hitherto been made exclusively prominent.

3. In the case of perfect identity between a present and

To a mathematical student this would be made at once intelligible by saying that in the former chapter the Contiguity is assumed as the vari able element, and the Similarity the constant; in this chapter, Similarity is supposed variable and Contiguity constant.