In his 1868 article for the Journal of Speculative Philosophy, ‘Some Consequences of Four Incapacities’, Charles Peirce lays out a systematic rejection of the principles of Cartesianism. His rationale consists of the assertion and defence of the ‘four incapacities’ of his title, four powers that the Cartesian tradition has in one way or another presumed to exist and which Peirce himself denies the philosophical inquirer (and by extension, the community of inquirers) to possess. Peirce summarises his anti-Cartesian quartet as follows:

1. 1. We have no power of Introspection, but all knowledge of the internal world is derived by hypothetical reasoning from our knowledge of external facts.

2. 2. We have no power of Intuition, but every cognition is determined logically by previous cognitions.

3. 3. We have no power of thinking without signs.

4. 4. We have no conception of the absolutely incognizable.

It is worth citing Peirce's defence of the fourth and final claim at some length since in it he raises a number of issues that will be crucial in what follows. Essentially, in justifying his rejection of any concept of the ‘absolutely incognizable’, Peirce moves from an initial conception of the mind-independent thing-in-itself that serves as a sort of ideal original limit of cognitive experience to a terminal understanding of the mind-independent real as a futural projection made on the basis of thought's presumptive tendency to exclude progressively the idiosyncratic aspects of individual cognitions. In other words, he orders the conceptual dynamics of thought itself in terms of a continuum or open interval stretched from the minimally to the maximally general, yet comprising neither endpoint within it.