which the levels of objective reality are determined. The level of objective reality is determined by the formal reality of what is being represented or thought about. So every idea I have has the lowest level of formal reality, for every idea is a mode, but the idea of an infinite substance has more objective reality than the idea of a finite substance. Kenny notes, “we sometimes use the word ‘reality’ to distinguish fact from fiction: on this view, the idea of a lion would have more objective reality than the idea of a unicorn since lions exist and unicorns do not. But this is not what Descartes means.” In this instance the idea of a lion and the idea of a unicorn would have the same objective reality because a lion and a unicorn (if it existed) would both be finite substances. Applying the causal adequacy principle Using the above ideas Descartes can claim that it is obvious that there must be at least as much reality in the cause as in the effect for if there wasn’t you would be getting something from nothing. He says “the idea of heat, or of a stone, cannot exist in me unless it is put there by some cause which contains at least as much reality as I conceive to be in the heat or in the stone. For although this cause does not transfer any of its actual or formal reality to my idea, it should not on that account be supposed that it must be less real.” Since the idea of God contains the level of (objective) reality appropriate to an infinite substance it is legitimate to ask where an idea with this level of reality came from. After considering various options Descartes concludes that it must come from a substance that has at least the same level of (formal) reality. Therefore, an infinite substance, i.e. God, must exist. Outline of Descartes' argument My ideas may be innate, adventitious (i.e. come from outside me), or have been invented by me. As yet I don't know their true origin. If ideas are considered simply as modes of thought, they are all equal and appear to come from within me; in so far as different ideas represent different things they differ widely. Ideas which represent substances contain within themselves more objective reality than the ideas which merely represent modes; the idea