Existanz?

I was reading ‘Zen and the art of motorcycle maintenance’ the other day and it got me thinking. What a thing has to do to exist????

Is it something it possesses? Some identifiable characteristic that one remembers, or keeps in his mind. I see a person X. I know he exists, cause I see him. But these are my eyes seeing him, my ears hearing him, my skin telling me something solid is in front of me. These are my senses giving me hints to someone’s existence. Or are they playing games with me? If my senses are cut off from my brain, then?

But this person X is a friend of mine. I’ve known him for quite a while. But not forever. Did he exist before I knew him. He sure did, but not for me! Its all in your head. The gray matter between your ears.

What about concepts then? Concepts exist. Concepts have always been there. Even before somebody had thought of them. Even before there was a ‘somebody’! Just waiting for an eager mind to sort out the web around it. So it flows that you don’t need to have a head pondering over something for it to exist. So it isn’t in your head.

What is it that I have done for you all to recognize my existence?

Ponderable??????