[471] Mind, xii, 67-74.
[472] Compare Bain's law of Association by Contiguity: "Actions, Sensations, and States of Feeling, occurring together or in close succession, tend to grow together, or cohere, 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" (Senses and Intellect, p. 327). Compare also Hartley's formulation: "Any sensations A, B, C, etc., by being associated with one another a sufficient Number of Times, get such a power over the corresponding Ideas a, b, c, etc., that anyone of the sensations A, when impressed alone, shall be able to excite in the Mind b, c, etc., the ideas of the rest." (Observations on Man, part i, chap. i, § 2, Prop. x.) The statement in the text differs from these in holding fast to the objective point of view. It is things, and objective properties in things, which are associated in our thought.
[473] Encyclopædia Britannica, 9th Ed., article Psychology, p. 60. col. 2.
[474] Physiol. Psych., 2d ed. ii, 300.
[475] The difficulty here as with habit überhaupt is in seeing how new paths come first to be formed (cf. above, [p. 109]). Experience shows that a new path is formed between centres for sensible impressions whenever these vibrate together or in rapid succession. A child sees a certain bottle and hears it called 'milk,' and thenceforward thinks the name when he again sees the bottle. But why the successive or simultaneous excitement of two centres independently stimulated from without, one by sight and the other by hearing, should result in a path between them, one does not immediately see. We can only make hypotheses. Any hypothesis of the specific mode of their formation which tallies well with the observed facts of association will be in so far forth credible, in spite of possible obscurity. Herr Münsterberg thinks (Beiträge zur exp. Psychologie, Heft i, p. 132) that between centres excited successively from without no path ought to be formed, and that consequently all contiguous association is between simultaneous experiences. Mr. Ward (loc. cit.) thinks, on the contrary, that it can only be between successive experiences: "The association of objects simultaneously presented can be resolved into an association of objects successively attended to.... It seems hardly possible to mention a case in which attention to the associated objects could not have been successive. In fact, an aggregate of objects on which attention could be focussed at once would be already associated." Between these extreme possibilities, I have refrained from deciding in the text, and have described contiguous association as holding between both successively and coexistently presented objects. The physiological question as to how we may conceive the paths to originate had better be postponed till it comes to us again in the chapter on the Will, where we can treat it in a broader way. It is enough here to have called attention to it as a serious problem.
[476] Essay, bk. ii, chap. xxxiii, § 6. Compare Hume, who, like Locke, only uses the principle to account for unreasonable and obstructive mental associations:
"'Twould have been easy to have made an imaginary dissection of the brain, and have shown why, upon our conception of any idea, the animal spirits run into all the contiguous traces, and rouse up the other ideas that are related to it. But though I have neglected any advantage which I might have drawn from this topic in explaining the relations of ideas, I am afraid I must here have recourse to it, in order to account for the mistakes that arise from these relations. I shall therefore observe, that as the mind is endowed with a power of exciting any idea it pleases; whenever it dispatches the spirits into that region of the brain in which the idea is placed, these spirits always excite the idea, when they run precisely into the proper traces, and rummage that cell which belongs to the idea. But as their motion is seldom direct, and naturally turns a little to the one side or the other: for this reason the animal spirits, falling into the contiguous traces, present other related ideas in lieu of that which the mind desired at first to survey. This change we are not always sensible of; but continuing still the same train of thought, make use of the related idea which is presented to us, and employ it in our reasoning, as if it were the same with what we demanded. This is the cause of many mistakes and sophisms in philosophy; as will naturally be imagined, and as it would be easy to show, if there was occasion."
[477] Op. cit. prop. xi.
[478] See Chapter III, [pp. 82-5].
[479] I strongly advise the student to read his Senses and Intellect, pp. 544-556.