Abstract

Often, when philosophical disputes about what is ultimately real reach a highwater mark of complexity, philosophers step back from the controversy to articulate rules which could settle the issues by showing us how to tell when a person is rationally required to posit an entity, i.e., to admit that it exists. I call such principles rules of rational positing. These rules come in two types, those that tend to make us posit more entities, and those that tend to make us posit fewer. The former are referred to as principles of plurality, the latter, principles of parsimony . ;Mediaeval philosopher Walter Chatton propounded a principle of plurality, which he opposed to William Ockham's famous principle of parsimony known today as 'the razor'. Chatton's principle is therefore sometimes called the 'anti-razor'; however, I have called it the 'Chatton Principle', following Chatton's own custom. The Chatton Principle states that, under certain conditions, we can reason from affirmative propositions to very sure conclusions about what must ultimately be real. ;Serious difficulties have arisen for specialists attempting to give an adequate interpretation of Chatton's principle and its underlying method. This dissertation gives an original interpretation of the Chatton Principle, which refutes the claim that Chatton's Principle and Ockham's razor are complimentary principles , refutes the claim that the method underlying the Chatton Principle is weak, and hence that the Principle is not a good rule but rather a 'magic wand', which multiplies entities needlessly, and subjects the corrected reading of the Chatton Principle to rigorous critique. My ultimate conclusion is that while the Chatton Principle is not lacking in logical force, it does not offer much general leverage against Ockhamism. However, Chatton's Principle does succeed against two particular applications of Ockhamist parsimony