_All thought is of this kind, an answer to a question._ Let us take the case of a scientific problem. Suppose that flints, which bear the marks of human workmanship, are found in a Pliocene bed, which has apparently remained undisturbed. The geologist is called upon to decide whether the deposit really has been undisturbed, so that the ‘find’ is reliable evidence of the existence of man in Tertiary times. The situation asks him a number of questions: has the bed been misplaced by faulting? can the materials have been brought to their present position by water? are there any signs that Quaternary man used the place? are the flints associated with bones of Tertiary animals? and so on and so forth. He forms a whole series of judgements; feature after feature of the situation is attended to, and every one in its turn is supplemented by ideas derived from previous knowledge; there is the familiar conflict of secondary attention, repeated over and over. Every judgement affirms or denies some property of the situation, in accordance with the original problem; and the outcome of the series of judgements, of the whole train of thought, is a final judgement,—still, of course, under the determination of the problem,—‘this bed has (or has not) been disturbed’. If the flints themselves are only doubtfully of human workmanship, then the situation is doubly complicated; the questions and the partial judgements are more numerous; but the general pattern of thought is the same. The tendency to dual division shows itself, then, in the form of the judgement, in the opposition of ‘subject’ to ‘predicate’; it shows itself further in the grammatical distinctions of substantive and adjective, verb and object, verb and adverb. And _all thought or reasoning seems to reduce, in the last resort, to a succession of judgements which, under the particular suggestion or determination, exhausts the possibilities of dual division_. The duality, however, is not always obvious at first glance. Ideas are involved; and the arousal of a particular idea may mean the excitement of a whole nest of associative tendencies; subject or predicate or both may thus be supplemented in manifold wise; and the train of thought may appear to be variously and irregularly divided. Only a careful observation will show that these supplementary processes derive, not directly from the suggestive situation, but rather from the secondary excitement of associative tendencies. Moreover, the judgements themselves are not always explicit; they may occur in nutshell form, as mental attitudes. _The tendency to dual division is thus masked in two ways: by incidental associations, and by attitudes._ It seems, nevertheless, to underlie the whole structure of thought.