As for their case for the possibility of seeing what is not a body, two arguments of theirs are well known. The first, which is the more widely known among them, is their claim that a thing must be seen either because it is coloured, because it is a body, because it is a colour, or because it exists. Sometimes they enumerate further grounds besides these.

They then say that it is false that a thing is seen because it is a body, since, if that were so, what is not a body would not be seen. It is likewise false that a thing is seen because it is coloured, since, if that were so, colour itself would not be seen. Nor is a thing seen because it is a colour, since, if that were so, a body would not be seen. They conclude that, once all these conceivable alternatives have been ruled out, the only remaining possibility is that a thing is seen because it exists.

The fallacy in this argument is evident: some things are visible in themselves, while others are visible by virtue of