A metaphysical question

The concept of being is so fundamental to philosophy that we usually take the idea of existence for granted rather than try to analyse its meaning. Philosophical confusions nevertheless lie in wait for thinkers in any branch of philosophy who have not first clarified what it means for something to exist. When the dust settles in these most basic of reflections in pure philosophical ontology, it appears that the definition of existence is transparently simple, although its implications are easily misinterpreted.

What exists? This is what we really want to know: whether and in what sense spatiotemporal physical entities, numbers and sets, propositions and universals, persons and minds and God, among other things, are real. Before we can address questions of what specific things or kinds of things exist, we need to understand the concept of existence, of being as such, or what Aristotle in the motto from Metaphysics Γ quoted in the epigraph refers to as being qua being or being as being, ον η ον. What is it, what does it mean, to be? This is the ultimate question for pure philosophical ontology. We cannot meaningfully assert the existence or nonexistence of physical entities, of numbers, sets, universals or anything else, unless or until we comprehend what it means for something to exist in the most general sense. The fact that the actual world exists is not generally in doubt, and perhaps cannot sanely be questioned.