In the Critique of So-called Practical Knowledge Alf Ross wishes to show that ethical judgments are nonsensical. He begins by asserting that when people speak about practical knowledge they mean knowledge which contains an unconditional command to the will, and this, he points out, involves a confusion between knowledge and volition. Thus, since all ethical theories are forms of practical knowledge, they are doomed to failure. All ethical theories can be classified into two types: they all belong to the ethics of value or the ethics of duty. These differ very radically, since the one takes value and the other duty as its fundamental concept; but they are inadequate for the same reasons. Both value and duty are self-contradictory concepts, and both awareness of value and awareness of duty are quite different from what ethical theories suppose.