The aim of this paper is to point out certain earlier features of Peirce's logical thought which have bearing upon his thesis that man is a sign. After the brief overview of the thesis itself, attention is paid to Peirce's concept of the "unity of symbolization" (part I) and its relation to Kant's "unity of apperception" (part II).
It is explained how Peirce understands apperception as bringing representations together, i.e. being represented together, and how this approach is in accordance with Peirce's general anti-psychological standpoint. The doctrine of man-sign is first seen as a result deduced from the hypothesis that laws of logic have primacy before the laws of the mind, and this result can then (part III) be seen as a further confirmation of that hypothesis.
By showing that there is no substantial difference between consciousness and other species of signs, Peirce is able to work out the notion of knowledge not bound to individual consciousness but to all-encompassing community of inquirers.