> Things exist. But then so do holes. How does a hole exist – it is defined by its surrounding solidities (earth, doughnut, wood etc). But if we can talk of the earth and the doughnut and the wood we know we are talking of something existing that is also physical. But there can be holes in arguments, in budgets, in understanding – again we know what arguments, budgets ad understanding are – though they are not physical. Mustn’t the opposite also exist? Mustn’t non-being also be, in order to identify what is?