This contradiction has been worked out in accurate and complete detail by Professor Jones.[30] He summarizes it as follows (p. 99): "No other way was left to him [Lotze] excepting this of first attributing all to sense and afterwards attributing all to thought, and, finally of attributing it to thought only because it was already in its material. This _seesaw_ is essential to his theory; the elements of knowledge as he describes them can subsist only by the alternate robbery of each other." We have already seen how strenuously Lotze insists upon the fact that the given subject-matter of thought is to be regarded wholly as the work of a physical mechanism, "without any action of thought."[31] But Lotze also states that if the products of the psychical mechanism "are to admit of combination in the definite form of a _thought_, they each require some previous shaping to make them into logical building-stones and to convert them from _impressions_ into _ideas_. Nothing is really more familiar to us than this first operation of thought; the only reason why we usually overlook it is that in the language which we inherit, it is already carried out, and it seems, therefore, to belong to the self-evident presuppositions of thought, _not to its own specific work_."[32] And again (Vol. I, p. 23) judgments "can consist of nothing but combinations of ideas which are no longer mere impressions: every such idea must have undergone at least the simple formation mentioned above." Such ideas are, Lotze goes on to urge, already rudimentary concepts--that is to say, logical determinations.