Concerning the law of association, very little has been learned since the time of Aristotle. It is determined by:
1. Similarity (the common quality of the symbol).
2. Contrast (because every image involves opposition between its extremes).
3. Co-existence, simultaneity (the being together of outer or inner objects in space).
4. Succession (images call each other out in the same order in which they occur).
Hume recognized only three grounds of association of objects—similarity, contact in time and space, and causality. Theo. Lipps recognizes as the really different grounds of association only similarity and simultaneity (the simultaneity of their presence in the mind, especially).
If, however, simultaneity is to be taken in this sense it may be considered the sole ground of association, for if the images are not simultaneous there can be no question of association. Simultaneity in the mind is only the second process, for images are simultaneous in the mind only because they have occurred simultaneously, existed in the same space, were similar, etc. Münsterberg,[211] who dealt with the matter and got important results, points out that all so-called inner associations, like similarity, contrast, etc., may be reduced to external association, and all the external associations, even that of temporal sequence, may be reduced to co-existence, and all co-existence-associations are psychophysically intelligible. Further: “The fundamental error of all association processes leading to incorrect connection of ideas, must be contained in their incompleteness. One idea was associated with another, the latter with a third, and then we connect the first with the third ... a thing we should not have done, since the first, while it co-existed with the second, was also connected with many others.”
But even this account does not account for certain difficulties, because some associations are simply set aside, although they should have occurred. Man is inclined, according to Stricker, to inhibit associations which are not implied in his “funded” complexes.
If we find direct contradiction with regard to associations, the way out is not easy. We have then, first, to consider how, by comparatively remote indirection, to introduce those conditions into the “funded” complex, which will give rise to the association. But such a consideration is often a big problem in pedagogy, and we are rarely in the position of teaching the witness.
There is still the additional difficulty that we frequently do not know the circumstance with the help of which the witness has made his association. Thomas Hobbes tells the story of an association which involved a leap from the British Civil War to the value of a denarius under the Emperor Tiberius. The process was as follows: King Charles I was given up by the Scotch for $200,000, Christ was sold for 30 denarii, what then was a denarius worth? In order to pursue the thread of such an association, one needs, anyway, only a definite quantity of historical knowledge, but this quantity must be possessed. But such knowledge is a knowledge of universal things that anybody may have, while the personal relations and purely subjective experiences which are at the command of an individual are quite unknown to any other person, and it is often exceedingly difficult to discover them.[212] The case is simplest when one tries to aid the memory of a witness in order to make him place single dates, e.g., when the attempt is made to determine some time and the witness is reminded of certain events that occurred during the time in question in order to assist him in fixing the calendar time. Or again, when the witness is brought to the place of the crime and the individual conditions are associated with the local situation. But when not merely single dates are to be associated, when complete events are to be associated, a profound knowledge of the situation must precede, otherwise no association is successful, or merely topsy-turvy results are attained. The difficulties which here ensue depend actually upon the really enormous quantity of knowledge every human being must possess in making use of his senses. Anything that a man has learned at school, in the newspapers, etc., we know approximately, but we have no knowledge of what a man has thought out for himself and what he has felt in his localized conditions, e.g., his home, his town, his travels, his relations and their experiences, etc.—However important this may be, we have no means of getting hold of it.