When I was eleven or twelve years old, I became for a while fixated on the question whether there could be two 'identical' stones. This is, of course, the question whether the principle of identity of indiscernibles is true and, as I formulated it then, I was bound to fall into confusion about it.

Metaphysics is the study of the most general nature and basic structure of reality, and therefore the concepts of metaphysics, concepts like time, space, identity, resemblance, substance, property, fact, event, composition, possibility, etc., are the most fundamental concepts. Thus metaphysics is the most fundamental theoretical discipline.

Those who take knowledge to be a whole zoo of sub-disciplines will react to my giving metaphysics a privileged position in that zoo or to my thinking of knowledge as a tree, with more and less fundamental parts.

The role of metaphysics in relation to other disciplines, whether philosophical or not and including the natural sciences, is thus a foundational role. Lack of clarity in the concepts of metaphysics implies lack of clarity in other disciplines - both theoretical and practical disciplines - employing those concepts or employing concepts that depend on those of metaphysics.

Although I felt I was quite good at criticising a philosophical position, I was not very good at defending and making a case for a philosophical position.

The problem of how to characterise the properties that would trivialise the principle is one of the hardest problems concerning the principle of identity of indiscernibles and one the problems to which least attention has been paid of.

Imperfect communities show that being a maximal resemblance class is not sufficient for being a property.