A derivative is something that does not exist on its own unless there is an underlying function (FUNCTION as in f(x)) that defines it at certain observations / delta points, now again don't go and think of the delta as the same delta as for the option Greeks, OK and get me into another loop of this go around the idiot conversation. See derivative as something that exist at certain points of time when the main function is stoped or observed so to say. The main function being the S&P 500, but that is not a tangible asset as it merely reflects the prices of the underlying stocks in the proportions that are held in it, so in turn itself is a derivative of the actual underlying prices of the individual stocks, the index becomes "tangible" tradable via the continuous futures contract, and SPX prices the options based on the changes on the index...