Experiments upon =generalisation=, that is, upon the positive abstraction of similars, have been made by the aid of meaningless forms, grouped as in the figure. The groups were of varying complexity, but always contained one common element; and the instruction given to the observer was that he should await the stimulus with as even as possible a distribution of attention, and then, when the figures appeared, should pick out the two that were alike. No less than six modes of procedure were distinguished. The observer might work actively through the forms, one by one; this is a laborious method, and was employed for the most part only in the early experiments of the series. Or he might travel over the groups, back and forth, until some figure struck him as familiar; this is the method of simple recognition. Or again he might start out on his journey of exploration, and find himself suddenly arrested by an insistent form, some figure that stood out more clearly than its fellows. Here are mixed methods, part active search and part passive impression. In other cases, the two forms stood out in quick succession, as if the one had drawn the other after it; in still other cases, the two similars stood out simultaneously, sprang forth as if of their own accord. Lastly, in rare instances, passivity reached its maximum; the observer looked at the field, was at once held by some outstanding form, and knew that this was the form required, although he had not remarked the presence of its pair. We cannot enter further into details; nor, indeed, is the time ripe for discussion; the experimental study of thought-procedures has hardly more than begun. You see, however, that _the pattern of thought may vary widely in certain of its features, while yet the outcome of thought, the abstraction or generalisation, is the same_; and this conclusion may help you to understand why there need be no specific mental pattern for the judgement. § 67. =Comparison and Discrimination.=—One of the commonest occurrences in a train of thought is the comparison of present with past, the harking back to a former stage of the procedure in order to make sure that we have not missed or mistaken some item of experience; and one of the commonest tasks set in the psychological laboratory reduces this comparison to its lowest terms. Two stimuli are presented, in succession; and the observer is required to say whether the intensity or quality of the corresponding sensations, the duration of the intervals, the magnitude of the forms, or whatever it may be, is the same or different. Both the stimuli themselves and the time which separates them may be varied in all sorts of ways; and the mental processes involved in the comparison vary accordingly. Here we shall mention only two points, which bear upon the course of thought at large.