Expressing the fundamental law in this most complicated way leads to the greatest ultimate simplification. Let us, for the present, only treat of spontaneous trains of thought and ideation, such as occur in revery or musing. The case of voluntary thinking toward a certain end shall come up later.
Take, to fix our ideas, the two verses from 'Locksley Hall':
"I, the heir of all the ages in the foremost files of time,"
and—
"For I doubt not through the ages one increasing purpose runs."
Why is it that when we recite from memory one of these lines, and get as far as the ages, that portion of the other line which follows, and, so to speak, sprouts out of the ages, does not also sprout out of our memory, and confuse the sense of our words? Simply because the word that follows the ages has its brain-process awakened not simply by the brain-process of the ages alone, but by it plus the brain-processes of all the words preceding the ages. The word ages at its moment of strongest activity would, per se, indifferently discharge into either 'in' or 'one.' So would the previous words (whose tension is momentarily much less strong than that of ages) each of them indifferently discharge into either of a large number of other words with which they have been at different times combined. But when the processes of 'I, the heir of all the ages,' simultaneously vibrate in the brain, the last one of them in a maximal, the others in a fading phase of excitement; then the strongest line of discharge will be that which they all alike tend to take. 'In' and not 'one' or any other word will be the next to awaken, for its brain-process has previously vibrated in unison not only with that of ages, but with that of all those other words whose activity is dying away. It is a good case of the effectiveness over thought of what we called on [p. 258] a 'fringe.'
But if some one of these preceding words—'heir,' for example—had an intensely strong association with some brain-tracts entirely disjoined in experience from the poem of 'Locksley Hall'—if the reciter, for instance, were tremulously awaiting the opening of a will which might make him a millionaire—it is probable that the path of discharge through the words of the poem would be suddenly interrupted at the word 'heir.' His emotional interest in that word would be such that its own special associations would prevail over the combined ones of the other words. He would, as we say, be abruptly reminded of his personal situation, and the poem would lapse altogether from his thoughts.
The writer of these pages has every year to learn the names of a large number of students who sit in alphabetical order in a lecture-room. He finally learns to call them by name, as they sit in their accustomed places. On meeting one in the street, however, early in the year, the face hardly ever recalls the name, but it may recall the place of its owner in the lecture-room, his neighbors' faces, and consequently his general alphabetical position; and then, usually as the common associate of all these combined data, the student's name surges up in his mind.
A father wishes to show to some guests the progress of his rather dull child in Kindergarten instruction. Holding the knife upright on the table, he says, "What do you call that, my boy?" "I calls it a knife, I does," is the sturdy reply, from which the child cannot be induced to swerve by any alteration in the form of question, until the father recollecting that in the Kindergarten a pencil was used, and not a knife, draws a long one from his pocket, holds it in the same way, and then gets the wished-for answer, "I calls it vertical." All the concomitants of the Kindergarten experience had to recombine their effect before the word 'vertical' could be reawakened.
Professor Bain, in his chapters on 'Compound Association,' has treated in a minute and exhaustive way of this type of mental sequence, and what he has done so well need not be here repeated.[479]