Abstract

Can we base the whole of logic solely on the concept of incompatibility? My motivation for asking this is two-fold: firstly, a technical interest in what a minimal foundations of logic might be; and secondly, the existence of philosophers who have taken incompatibility as the ultimate key to human reason (viz., e.g., Hegel's concept of determinate negation). The main aim of this contribution is to tackle two related questions: Is it possible to reduce the foundations of logic to the mere concept of incompatibility? and Does this reduction lead us to a specific logical system? We conclude that the answers, respectively, are YES and a qualified NO (qualified in the sense that basing semantics on incompatibility does make some logical systems more natural than others, but without ruling out the alternatives.) A search for the bare bones of logic generally leads one to the relation of inference (or consequence). This way is explored meticulously by Koslow (1992). He defines an implication structure as, in effect, an ordered pair , where S is a set and | f Pow(S)HS fulfilling certain (relatively simple) restrictions. And obviously if we reduce incompatibility to inference, which is achievable by the well known ex contradictione quodlibet principle, we reach a logic based on incompatibility. The kind of logic flowing most straightforwardly from this setting is the intuitionist one. However, there is also the approach taken by R. Brandom and A. Aker (2008), who have set up a logic based directly on incompatibility. They define an incompatibility structure as an ordered pair such that S is a set and z f Pow(S) (again fulfilling certain restrictions). The authors introduce logical operators in such a way that they reach classical logic. Does this mean that inference 'naturally' leads to intuitionist logic, whereas incompatibility leads to the classical one? Myself, I have argued that it is indeed intuitionist logic that is the logic of inference (see Peregrin, 2008)..