In the same person, the same word heard at different times will provoke, in consequence of the varying marginal preoccupations, either one of a number of diverse possible associative sequences.  Professor Muensterberg performed this experiment methodically, using the same words four times over, at three-month intervals, as ‘cues’ for four different persons who were the subjects of observation.  He found almost no constancy in their associations taken at these different times.  In short, the entire potential content of one’s consciousness is accessible from any one of its points.  This is why we can never work the laws of association forward:  starting from the present field as a cue, we can never cipher out in advance just what the person will be thinking of five minutes later.  The elements which may become prepotent in the process, the parts of each successive field round which the associations shall chiefly turn, the possible bifurcations of suggestion, are so numerous and ambiguous as to be indeterminable before the fact.  But, although we cannot work the laws of association forward, we can always work them backwards.  We cannot say now what we shall find ourselves thinking of five minutes hence; but, whatever it may be, we shall then be able to trace it through intermediary links of contiguity or similarity to what we are thinking now.  What so baffles our prevision is the shifting part played by the margin and focus—­in fact, by each element by itself of the margin or focus—­in calling up the next ideas.

For example, I am reciting ‘Locksley Hall,’ in order to divert my mind from a state of suspense that I am in concerning the will of a relative that is dead.  The will still remains in the mental background as an extremely marginal or ultra-marginal portion of my field of consciousness; but the poem fairly keeps my attention from it, until I come to the line, “I, the heir of all the ages, in the foremost files of time.”  The words ‘I, the heir,’ immediately make an electric connection with the marginal thought of the will; that, in turn, makes my heart beat with anticipation of my possible legacy, so that I throw down the book and pace the floor excitedly with visions of my future fortune pouring through my mind.  Any portion of the field of consciousness that has more potentialities of emotional excitement than another may thus be roused to predominant activity; and the shifting play of interest now in one portion, now in another, deflects the currents in all sorts of zigzag ways, the mental activity running hither and thither as the sparks run in burnt-up paper.

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One more point, and I shall have said as much to you as seems necessary about the process of association.