Well, Jack, I think that anything which is sentient is alive. I don't think that's the only way of being alive, some live things probably aren't sentient...but I do think that everything which is sentient is alive...otherwise it wouldn't be sentient at all. It thinks, therefore it is.

I would include transdimensional beings, or what we might term "spirits", for instance, among things that are sentient...though they might not exist physically in our terms.