Elbert Booij

Two semantic paradoxes, the Liar and Curry’s paradox, are analysed using a newly developed conception of procedural semantics (semantics according to which the truth of propositions is determined algorithmically), whose main characteristic is its departure from methodological realism. Rather than determining pre-existing facts, procedures are constitutive of them. Of this semantics, two versions are considered: closed (where the halting of procedures is presumed) and open (without this presumption). To this end, a procedural approach to deductive reasoning is developed, based on the idea of simulation. As is shown, closed semantics supports classical logic, but cannot in any straightforward way accommodate the concept of truth. In open semantics, where paradoxical propositions naturally ‘belong’, they cease to be paradoxical; yet, it is concluded that the natural choice—for logicians and common people alike—is to stick to closed semantics, pragmatically circumventing problematic utterances.

Kinds - also known as 'natural sets' or 'universals' - are a very intuitive assumption about the way the world is put together. As a piece of metaphysical theory, however, they give rise to the Identification Problem: which of all sets are the ones that in fact qualify as kinds? In this thesis an answer is given starting out from the assumption that kindhood always coincides with similarity. From this it follows that similarity must be similarity 'with respect to', and p properties - kinds - must be arranged in 'similarity systems'. To turn this insight into a credible answer to the Identification Problem, however, a wide variety of (physical) objects must be considered, whose common ground is that they are all 'mereologically complex'. Therefore in the second part of the thesis the focus will be on the derivation of 'composite kinds', thus allowing the classification of larger objects in terms of kinds. It will be concluded that classical (Boolean) mereology is sufficient for this purpose. I shall argue that this approach is therefore preferable to that whereby kinds are reified to be (structural) universals