If all knowledge is a kind of belief, then what is not believed is not known; just as if all men are animals, what is not an animal is not a man. But we can know something without believing it: e.g. the meaning of a word.
If knowledge is a species of belief, what is the specific difference? If the difference is something known, then a difference would be the same as the species, which is impossible; if the difference is something unknown, then knowledge would be something unknown, which is impossible.
If knowledge is a kind of belief, then a faculty by which we know is a kind of faculty by which we believe. But we know by intellect producing assent, and believe by will producing assent; and intellect is not a kind of will, but rather the two are separate powers.