Choose one of the elements defended by the pre-Socratic philosophers (water, fire, numbers, and so on) and argue for it as well as you can, preferably with a friend or a few friends who will try to prove you wrong. For example, if you choose fire, an immediate objection would be that fire could not possibly be the essential element in cold objects—a block of ice, for example. A reply might be that cold objects simply contain much less fire than hot things. You might also argue that not all fire manifests itself as flame, and soon, no doubt, you will find yourself moving into more modern-day talk about energy instead of fire as such. The point of the exercise is (1) to see how very much alive we can still make these ancient theories in our own terms and (2) to show how any theory, if it has even the slightest initial plausibility, can be defended, at least to some extent, if only you are clever enough to figure out how to answer the various objections presented to you and modify your theory to meet them.