  Although there are many examples of phenomena that do seem more or less naturally to divide into three groups, Peirce seems to have been driven by something more than mere examples in his insistence on applying his categories to almost everything imaginable. Perhaps it was the influence of Kant, whose twelve categories divide into four groups of three each. Perhaps it was the triadic structure of the stages of thought as described by Hegel. Perhaps it was even the triune commitments of orthodox Christianity (to which Peirce, at least in some contexts and during some swings of mood, seemed to subscribe). Certainly involved was Peirce’s commitment to the ineliminability of mind in nature, for Peirce closely associated the activities of mind with the aforementioned triadic relation that he called the “sign” relation. (More on this topic appears below.) Also involved was Peirce’s so-called “reduction thesis” in logic (on which more will given below), to which Peirce had concluded as early as 1870.