Alexander James Bird

1.Following Kripke, many philosophers have accepted the existence of propositions concerning essences, and, more generally, propositions asserting necessities, that are knowable only a posteriori. Such an acceptance is consistent with the claim that ultimately all knowledge of necessity is a priori. A posteriori knowledge of necessity may be held to be a consequence of the combination of a priori knowledge of a proposition asserting essence or necessity with a posteriori knowledge of a non-modal proposition. E. J. Lowe (2007: 287–88) denies even this kind of derived a posteriori knowledge of essence or necessity. He reconstructs the form of an argument that is intended to lead to a proposition concerning essence but which is known a posteriori: This schema may be exemplified thus: As this example illustrates, instances of (1) are a priori propositions concerning essence, while instances of (2) are a posteriori propositions; instances of the conclusion are propositions asserting particular essences, and are, it is claimed, knowable only a posteriori.1.

We talk as if there are natural kinds and in particular we quantify over them. We can count the number of elements discovered by Sir Humphrey Davy, or the number of kinds of particle in the standard model. Consequently, it looks at first sight at least, that natural kinds are entities of a sort. In the light of this we may ask certain questions: is the apparent existence of natural kinds real or an illusion? And if real, what sort of entity are natural kinds? Are they sui generis? Or can they be identified with or reduced to some other kind of entity? In this essay I shall look at possible reasons for asserting that either kinds are no sort of entity, or, if they are entities, their existence is equivalent to some fact not involving kinds. Richard Boyd seems to take the view that the apparent existence of natural kinds is an illusion.

I defend against criticism the following claims concening Thomas Kuhn: (i) there is a strong naturalist streak in The structure of scientific revolutions, whereby Kuhn used the results of a posteriori enquiry in addressing philosophical questions; (ii) as Kuhn's career as a philosopher of science developed he tended to drop the naturalistic elements and to replace them with more traditionally philosophical a prior approaches; (iii) at the same there is a significant residue of positivist thought in Kuhm, which Kuhn did not recognise as such; (iv) the naturalist elements referred to in (i) are the most original and fruitful elements of Kuhn's thinking; (v) the positivistic elements referred to in (iii) vitiated his thought and acted as factors in preventing Kuhn from developing the naturalistic elemtns and from following the path taken by much subsequent philosophy of science. Preston presents an alternative reading of Kuhn which emphasizes the Wittgensteinian elements in Kuhn. I argue that this alternative view is, descriptively, poorly supported by the textual evidence and the facts of the history of philosophy of science in the twentieth century. I provide some defence of the naturalistic approach and related themes.

When is a belief or judgment justified? One might be forgiven for thinking the search for single answer to this question to be hopeless. The concept of justification is required to fulfil several tasks: to evaluate beliefs epistemically, to fill in the gap between truth and knowledge, to describe the virtuous organization of one’s beliefs, to describe the relationship between evidence and theory (and thus relate to confirmation and probabilification). While some of these may be held to overlap, the prospects for fulfilling all may well seem poor. Furthermore the internalist requires that justification be an introspectible property of beliefs and a fundamental epistemic concept, while the externalist is often happy to ignore the concept altogether or at best regard it as an embarrassing add-on to their epistemology. In the light of this one might reasonably give up on justification altogether or adopt pluralist approach, denying that justification is any single property of beliefs of judgments.