The Commens Dictionary
Quote from ‘A Brief Intellectual Autobiography by Charles Sanders Peirce’
Secondness is that mode or element of being by which any subject is such as it is in a second subject regardless of any third; or rather, the category is the leading and characteristic element in this definition, which is prominent in the ideas of dyadic relativity or relation, action, effort, existence, individuality, opposition, negation, dependence, blind force. Secondness has two grades, the genuine and the degenerate (just as a pair of rays is called a “degenerate” conic) and this is true in several ways. Every genuine secondness has two correlative aspects, of which one is more active or first, the other more passive or second; and these two together make a total secondness between two correlative subjects.
This quote has been taken from Kenneth Laine Ketner's 1983 reconstruction of Peirce's 'Autobiography'