Digital Companion to C. S. Peirce
1867 | On a New List of Categories | W 2:50; CP 1.549

Dissociation is that separation which, in the absence of a constant association, is permitted by the law of association of images. It is the consciousness of one thing, without the necessary simultaneous consciousness of the other.

1885 | Notes on the Categories [R] | W 5:238; CP 1.353

…two ideas may be so little allied that one of them may be present to the consciousness in an image which does not contain the other at all; in this way we can imagine red without imagining blue, and vice versa; we can also imagine sound without melody, but not melody without sound. I call this kind of separation Dissociation.

1903 | Syllabus: Syllabus of a course of Lectures at the Lowell Institute beginning 1903, Nov. 23. On Some Topics of Logic | EP 2:270

Separation of Firstness, or Primal Separation, called Dissociation, consists in imagining one of the two separands without the other. It may be complete or incomplete.