When you say that a thing is bad you use the criterium of good.

Argument from error. If matter be truth it is impossible to err, sensation cannot lead us wrong. (Now error either comes from sensation proper or from reasoning. Both of these, according to the materialists, are natural. The principle of error cannot then be in either of them.

Error supposes two things, two principles — one fallible, the other infallible. It supposes an infallible principle because it were not error unless there were a truth to which it might be opposed. It supposes for its existence a principle to which fallibility can be attributed. It supposes, in short, a principle of possibility and a principle of existence.