I think you need to make your question more specific. Why do people buy instead of bartering or instead of being self-sufficient? The answer to that question lies in the power of divided labor and the convenience of having an agreed upon medium of exchange that is easily portable. Given that, why do people buy food, clothing, shelter? Well, because they need to in order to survive. Why do they buy things that are not necessary? Well, that's a more difficult question, with multiple answers depending upon what items are being considered. You could also be asking how people decided what things to buy, which is again a very different question from the others. So, what are you asking, exactly?
Sean, EssayForum.com