In phenomenology, [Peirce] is of opinion that there are two sets of categories, a long list and a short one; and he admits that there may possibly be still others. Though he devoted two years to the study of the long list, he attained no satisfactory results. The shorter list is called by [the] easily remembered designation of the cenopythagorean categories. These are Firstness, Secondness, and Thirdness.