Peirce wrote: Thus, in brief, my philosophy may be described as the attempt of a physicist to make such conjecture as to the constitution of the universe as the methods of science may permit, with the aid of all that has been done by previous philosophers... Demonstrative proof is not to be thought of. The demonstrations of metaphysicians are all moonshine. The best that can be done is to suppl...

Charles S. Peirce argued that, besides deduction and induction, there is a third mode of inference which he called "hypothesis" or "abduction". He characterized abduction as reasoning "from effect to cause", and as "the operation of adopting an explanatory hypothesis". Peirce's ideas about abduction, which are related also to historically earlier accounts of heuristic reasoning (the method of a...

Peirce believed that his pragmaticism can be conclusively proven. Beginning in 1903, he drafted several attempts, ending by 1908 with a semeiotic proof. Around 1905, he exposes the proof using the theory of Existential Graphs (EGs). This paper modernises the semantics Peirce proposed for EGs in terms of game-theoretic semantics (GTS). Peirce’s 1905 proof is then reconstructed in three parts, by...

Peirce developed an analysis of reality that defined reality – all forms of reality, whether chemical, biological or social as existing in Signs. A sign is a spatiotemporal reality, material or conceptual, that exists in relations with other signs, as in “I use the word “Sign” in the widest sense for any medium for the communication or extension of a From (or feature). Being medium, it is deter...

This paper develops and compares two tableaux-style proof systems for Peirce algebras. One is a tableau refutation proof system, the other is a proof system in the style of Rasiowa-Sikorski.