Everything must necessarily exist mustn't it?

I've been thinking about the term existence. Sometimes we wonder if reality exists but by the fact that we are discussing it, I argue that it must exist. Now, I'm not saying it must be the whole story but if we ume reality is an illusion, it must exist as one, right? I mean we don't say "dreams do not exist" just because they are thoughts do we? You might call this semantics but I think that this breaks down a barrier between the material and the abstract which we always consider an axiom. Also things can't exist at different levels, existence is simply the state of being. So mustn't everything necessarily exist in some form which we perceive in different qualities?