# 7 Challenging the paradigm

In this chapter we raise our heads from the technical details of operating the calculus of first order logic and take a fresh look at the system. We consider some arguments to the effect that "classical" logic is flawed in that it is based on an over-hasty and over-simplified account of what arguments are. It is at least interesting to look at alternative views and the kinds of logic to which they might give rise. A full investigation of non-classical logic is far beyond the scope of these notes, but the existence of other paradigms needs to be noted and some of the flavour of such "deviant" logics needs to be brought out.

We note three non-classical propositional logics, and conclude with some notes on their semantics. While we do not detail the semantic theories in full, we do look briefly at a semantic technique for showing classically valid sequents to be invalid by the lights of some of the alternative systems.

- Paradoxes of Implication Relating logic and language: the case of relevant logic
- Vagueness Thoughts on the sorites paradox and fuzzy logic
- A constructive view of truth A quick look at intuitionist logic
- Modelling non-classical logic Using 3-valued semantics to disprove sequents