Philosophy: Where Science and Magic Are Born

Now it is indeed evident by the light of nature that there must be at least as much [reality] in the efficient and total cause as there is in the effect of that same cause. For whence, I ask, could an effect get its reality if not from its cause? And how could the cause give that reality to the effect, unless it also possessed that reality? Hence it follows that something cannot come into being out of nothing, and also that what is more perfect (that is, what contains in itself more reality) cannot come into being from what is less perfect. But this is manifestly true not merely for those effects whose reality is actual or formal, but also for ideas in which only objective reality is considered. For example, not only can a stone which did not exist previously not now begin to exist unless it is produced by something in which there is, either formally or eminently, everything that is in the stone; nor heat be introduced into a subject which was not already hot unless it is done by something that is of at least as perfect an order as heat - and the same for the rest - but it is also true that there can be in me no idea of heat, or of a stone, unless it is placed in me by some cause that has at least as much reality as I conceive to be in the heat or in the stone. For although this cause conveys none of its actual or formal reality to my idea, it should not be thought for that reason that it must be less real. Rather, the very nature of an idea is such that of itself it needs no formal reality other than what it borrows from my thought, of which it is a mode. But that a particular idea contains this as opposed to that objective reality is surely owing to some cause in which there is at least as much formal reality as there is objective reality contained in the idea. For if we assume that some thing is found in the idea that was not in its cause, then the idea gets that something from nothing. Yet as imperfect a mode of being as this is by which a thing exists in the intellect objectively through an idea, nevertheless it is plainly not nothing; hence it cannot get its being from nothing.
-Rene Descartes, "Meditations on First Philosophy", Meditation Three.

I find this passage, and much of the rest of the text it was taken from, to have interesting implications for magical practitioners with a somewhat scientific bent. If you do too, you might also find "The Ethics" by Baruch Spinoza equally intriguing. I recently had occasion to read through the former, and at least skim the latter.