Opening plenary talk: Recent advances in metaphysics

In some quarters, the expression 'advance in metaphysics' may soundlike a contradiction in terms, a widespread assumption being thatprogress is never really made in philosophy, in the way that it isin the empirical sciences. But a discipline need not be empiricalin order to be capable of progress, as the case of mathematicsdemonstrates. Even so, metaphysics may be thought to compareunfavourably with mathematics, because there is far less consensusamongst its practitioners than there is amongst mathematicians.This, however, is unsurprising, given that metaphysics addressesthe most difficult questions that confront the human mind,concerned as it is with the fundamental structure of reality as awhole. Central to that concern is ontology, the science of being.And central to ontology is category theory. This is an area ofphilosophy in which advance most certainly has been made in recentyears and one which has much potential for fruitful practicalapplicationOntological categories are categories of being, notcategories of thought. Ontology is the science of being, not thescience of our thought about being. Many philosophers andnon-philosophers are tempted to think otherwise because they areconsciously or unconsciously influenced by the pervasive relativismand anti-realism of the current intellectual climate. They arepersuaded that we can know nothing about the structure of reality'as it is in itself,' and so must retreat to contemplation of thestructure of our thoughts about reality. This is a position that isat once defeatist and internally inconsistent. If we canlegitimately aspire to any sort of knowledge at all, we can andmust aspire to some knowledge of the structure of reality. At thesame time, we must forgo any claim to infallibility in this or anyother branch of knowledgeOntological categories are differentiatedby the distinctive existence- and identity-conditions of theirmembers. A fundamental ontological category is one whose membershave existence- and identity-conditions which are not exhaustivelyspecifiable in terms of ontological dependency relations betweenthose members and the members of other ontological categories. Itis a matter of debate how many, and which, fundamental ontologicalcategories should be recognised. Some contemporary metaphysiciansfavour an ontology which recognises only one fundamentalontological category, that of so-called 'tropes,' or individualproperty- and relation-instances. Others favour a two-categoryontology comprising, on the one hand, properties and relationsconceived as universals and, on the other, individual bearers ofproperties, that is, individual 'objects' or 'substances.' A thirdoption is a four-category ontology which recognises as fundamentaltwo categories of particulars (individual property- andrelation-instances, and individual substances) and two categoriesof universals (properties and relations, and substantial kinds).Each of these rival ontologies has some claim to provide the bestmetaphysical foundation for natural science. What cannot bedisputed is that recent debate between their adherents has beenhealthy and has led to genuine progress in our attempts to graspthe fundamental structure of reality.