1. Everyone agrees they exist. 2. Your turn . . . .
I'm fairly sure no one here agrees with Descartes. But, hmmmmm. I am fairly sure that there'd be a great disagreement about what actually is a thought, so we'd have to have that sussed out firstly before we put Descartes before us horses....heh. Even if it is argued that we are but constructs in an immense cosmic computer, still, that is a form of existence, but the term "alive" now becomes debatable. Hmmmmm. By the way: Is a ghost alive? I agree that I exist as an non-entity -- a semantic designation, but it's about as ephemeral as I can get with words.
