It seems obvious that I could have failed to exist. My parents could easily never have met, in which case I should never have been conceived and born. The like applies to everyone. More generally, it seems plausible that whatever exists in space and time could have failed to exist. Events could have taken an utterly different course. Our existence, like most other aspects of our lives, appears frighteningly contingent. It is therefore surprising that there is a proof of my necessary existence, a proof that generalizes to everything whatsoever. I will explain the proof and discuss what to make of it. A first reaction is that a ‘proof of such an outrageous conclusion must contain some dreadful fallacy. Yet the proof does not collapse under scrutiny. Further reflection suggests that, suitably interpreted, it may be sound. So interpreted, the conclusion is not outrageous, although it may not be the view you first thought of.

1. The proof rests on three main claims. The first is that my nonexistence strictly implies the truth of the proposition which states my nonexistence:

1. (1) Necessarily, if I do not exist then the proposition that I do not exist is true.

For that things are so-and-so is just what it takes for the proposition that they are so-and-so to be true. The second main claim is that the truth of the proposition strictly implies its existence:

1. (2) Necessarily, if the proposition that I do not exist is true then the proposition that I do not exist exists.