I think, therefore I am;
You act, therefore you might be.

I'm a human being;
You're a human doing.

Now you can say the same in reverse.

Talk to yourself about who you are. Talk to others about what you do, or who you are in terms of what you do. This is all that can have meaning for them. We depend more on our own peceptions than on what people tell us. We need to be able to varify with our own senses. Like with sub-atomic particles, we can observe a person's appearance, location and actions. We can't directly observe who the person really is. Only the person himself can hope to know that. We can't directly observe another person's mind, soul, thoughts or "being". Therefore we can't say for sure that "he" has a mind, anymore than we can say that a computer or an animal doesn't. (Anyway, it's more in terms of what level of mind they have.) We can only try to measure the complexity of their actions and information processing abilities. Perhaps the "conscious mind" is no more significant than the information I see on my computer screen, with the real "thinking" going on behind the scenes. See thoughts on Consciousness etc.