By ‘the nature of being’ (which is the subject of ‘ontology’) we mean first the nature of ‘beings’. What sorts of things are there? Material objects, for one, as occupiers of space-time. Beyond them (or instead of them) there may be such further things as events, states of affairs, persons, numbers, ideas, qualities, waves. As well as asking about beings, we may ask what ‘being’ itself is. Plato and Heidegger take this question to be very important; Aristotle and many others think it is senseless and so needs no answer — Professor Jonathan Dancy