By retentiveness Bain means both the temporary persistence of a sensory impression after the withdrawal of the stimulus and the coherence of actions, sensations, and states of feeling occurring together or in close succession, ' in such a way that, when any one of them is afterwards presented to the mind, the others are apt to be brought up in idea.' This is the Law of Contiguity, which is said to be the basis of all memory, habit, and acquired power. The law thus not only stands for the tie between items of experience, which tie presupposes retentiveness of the experiences, but it also includes the fact of retentiveness itself.

The seat of the sensation and of the image are regarded as the same, a physiological doctrine which supports the theory that the two differ in degree not in kind.

The old notion supposes that the brain is a sort of receptacle of the impressions of sense, where they lie stored up in a chamber quite apart from the recipient apparatus, to be manifested again to the mind when the occasion calls. The idea of a cerebral closet shut off, is quite incompatible with the real manner of the working of nerve. Since, then, a sensation, in the first instance, diffuses nerve currents through the interior of the brain outwards to the organs of expression and movement-the persistence of that sensation after the outward exciting cause is withdrawn can be a continuance of the same diffusive currents, perhaps less intense but not otherwise different. . . . Now if this be the case with impressions persisting when the cause has ceased, what view are we to adopt concerning impressions reproduced by mental causes alone, or without the aid of the original, as in ordinary recollection?... There is only one answer that seems admissible. The renewed feeling occupies the very same parts, and in the very same manner, as the original feeling, and no other parts, nor in any other assignable manner.' (ibid., pp. 355, 356.)

Presumably Bain, like his predecessors--and, one may add, his successors-finds the explanation of association and revival in physiology. The Law of Contiguity is an axiom for Psychology, as is also the Law of Similarity: Present actions, sensa

tions, thoughts or emotions, tend to revive their like among previous impressions, or states.' For Bain consciousness of likeness and consciousness of difference presuppose a supply of discrete items brought before the mind by the play of association or by the course of events in the external world. Yet by the Law of Similarity 'likeness' is treated as the occasion for the presence in consciousness of that which logically the consciousness of likeness may be said to presuppose. Can that which is treated as a condition for the appearance of previous experience in consciousness be also regarded as a cognitional relation between items of experience? This is a point to which the criticism of later writers, and in particular that of Prof. Ward, was directed.

In the detailed treatment of memory Bain is in advance of any of his predecessors. He discusses the influence of age, fatigue, and repetition on retentiveness, and he considers the differentiae of sensations and ideas. They are said to differ in force, vividness, intensity; the one is a strong effect, the other a weak. He suggests that

'In cases where a sensation has physical consequences, we might measure, from the physical side, the comparative strength of the sensation and the idea. Thus the contact of food with the tongue and cheek causes a flow of saliva; so does the idea or anticipation. But the flow under the sensation is at least several times greater than the flow under the idea.' (Emotions and Will, p. 565.)

In view of Pavlow's experiments this is an interesting suggestion. Ideas are said to differ from sensations in lack of detail, lack of steadiness; further they are less able to hold the mind's regard and exclude other states. They are in fact for Bain comparable to weak sensations.

Bain agrees with James Mill, in opposition to John Stuart Mill, that the difference between memory and imagination can be shown by an analysis of content known.

'The principal distinction between Memory and Imagination

lies in the setting of the respective ideas. Ideas of Memory have a place in the continuous chain of our remembered life : ideas of Imagination correspond to nothing in that chain, or rather, they are consciously combined from different ideas of Memory taken out of their Memory setting, and aggregated under a special motive.' (ibid., p. 534.)

Bain, however, emphasized the importance of volition in Belief. Indeed, he wrote in his earlier editions as if Belief itself were a special form of volition, not derivable from either emotional or intellectual consciousness. Preparedness to act on what we affirm is the mark of Belief. Bain credits the human mind with a primitive credulity. Ideas have a tendency to become sensations. This is of course true in a literal sense for ideas of movement; Bain regards it as true of all ideas, and, although experience educates this primitive credulity, the ideas brought before the mind by retentiveness working under the Law of Contiguity will retain their bias to sense validity. This is in effect Bain's solution of the problem of why Belief is present in memory but may be absent in imagination. It is on the lines of James Mill's and is in keeping with the analysis of the difference between memory and imagination; it is, in a word, consistent with Associationism.

Biological conceptions dominate Psychology in Herbert Spencer's Principles of Psychology, which was published in the same year as Bain's Senses and Intellect. His psychology is part of an evolutionary system of philosophy. In the gradual evolution of life the psychical is differentiated from the physical, but the two function as one in that 'continuous adjustment of internal relations to external relations' wherein life consists. Instinct and memory represent two stages of development; that is, stages in the organization of correspondence between organism and environment. Instinct stands for the co-ordinated reflexes established by accumulated experiences; memory, for varying connexions met with in the course of experience.

'Let it be granted that the more frequently psychical states occur in a certain order, the stronger becomes their tendency to cohere in that order, until they at last become inseparable; let it be granted that this tendency is, in however slight a degree, inherited, so that if the experiences remain the same each successive generation bequeaths a somewhat increased tendency; and it follows that there must eventually result an automatic connexion of nervous actions, corresponding to the external relations perpetually experienced.' (Principles of Psychology, 3rd ed., pt. 4, ch. v, p. 439.)

Instinct may be regarded as a kind of organized memory; on the other hand, memory may be regarded as a kind of incipient instinct.' (ibid., ch. vi, p. 445.)1

In the sphere of action, when the impressions serving as stimuli to special actions become complicated, automatic response is impossible. There is on the one hand a greater time requisite for the reception of the impression, this involves persistence, and further the complicated impression arouses more than one reflex response; these responses become nascent before the appropriate response to the particular set of stimuli is made.

'These nascent nervous excitements that conflict with one another, are really so many ideas of the motor changes which if stronger they would cause; or rather they are the objective side of those changes which are ideas on their subjective sides. Consequently, Memory necessarily comes into existence whenever automatic action is imperfect.' (ibid., p. 448.) In the sphere of knowledge,

'As the external groups of attributes and relations responded to become more complex, and by implication more infrequent, the answering physical changes become more loosely connected with one another and with the motor changes appropriate to them. . . . Most of these surrounding

I How far Spencer is here preaching the same doctrine as Butler is an open question. Butler asserts that prior to his own teaching Spencer did not recognize that the phenomena of heredity were phenomena of memory, and did not make memory the keystone of his system. (See Luck, or Cunning? ch. i, 1, 2.)

things, however, have no immediate relations to the needs of the organism-are not habitually followed by special motor changes; and therefore do not tend to excite motor changes. But while the clustered psychical states produced by the clustered properties of inanimate objects have usually no direct connexions with the actions, they have direct connexions with one another of all degrees of constancy; and, by consequence, have all degrees of the tendency to rouse one another. While the absolutely persistent relations among external attributes are responded to by inseparable relations of psychical states; the others, in their respective grades of persistence, are responded to by psychical states proportionate in their degrees of cohesion. Hence, of the impressions produced by adjacent objects during the movements of the organism, each is apt to make nascent certain other impressions with which it has been connected in experience-calls up ideas of such other impressions; that is, causes a remembrance of the attributes previously found in connexion with the perceived attributes. As these psychical states have in their turns been connected with others, they tend to arouse such others; and thus there arises that succession of ideas, partly regular, and partly irregular, which we call Memory-regular in so far as the connexions of external phenomena are regular, and irregular in so far as the groups of these phenomena occur irregularly in the environment.' (ibid., pp. 449, 450.)

As soon as any connexions among psychical states through constant repetition become fixed and automatic, they cease to be part of memory. Common knowledge, such as that fire burns and the sun shines, are organizations which have ceased to be memory. It is thus that Spencer arrives at his ultimate test of the validity of any proposition, the 'universal postulate' behind which thought cannot go; viz., the inconceivability of the opposite. When a connexion has become fixed and automatic through repetition,

To assert the inconceivability of its negation is at the same time to assert the psychological necessity we are under of thinking it, and to give our logical justification for holding it to be unquestionable. (ibid., pt. 7, ch. xi, p. 407.) Memory then pertains to that class of physical states which are in process of being organized.' (ibid., pt. 4, ch. vi, p. 452.)