You: Imagine that the sand I am digging in is on a far away planet in another solar system, and that the object I find seems to be a simple but completely alien tool. After a little experimentation, I discover that it can be used either to kill an enemies or to make boards into planks. There is no way that I can tell what it was originally designed for, or even if it was designed to do either of these things. In fact, it may not have been designed at all and we may be simply finding uses for an undesigned thing. If we cannot tell what the purpose, if any, of an object is, then we cannot prove that it was designed.

Aaron: A rock may be used as a hammer or a tool for killing although it was not designed to be either, but a more complex thing will obviously have a purpose even if we do not know what it is. If the alien tool you found had writing engraved on it or was cast from metal, then you would certainly know that it had been designed for something, even though you may not be able to tell what that something was.

You: I agree with you on that point, but I don't see how it helps your argument. By the pocket watch analogy, you are trying to show that complex things imply a designer, not that things that look like human artifacts imply a designer. If I came upon an animal on an alien planet that ate sand and secreted glass, I would not assume that it had been designed by an alien intelligence for that purpose.

Aaron: Well, it couldn't very well have just sprung up out of the dust on its own.

You: True, but science allows for the evolution of very complex creatures over long periods of time and does not require an intelligent being to have any part in it.

Aaron: Then your science is wrong.