It seems a reasonable hypothesis, doesn't it? I am prepared to admit that you *probably* exist even when I have no current perceptions of your actions or effects.
Although who knows, maybe you will claim that you exist only at those moments that I happen to perceive you...
Maybe you will claim that none of us existed until 3:15 PM EST on November 3, 1999, and that we were created with the memories of our previous existence...
Brad DeLong