 The Academics used these arguments to point out that if our impressions are never self-warranting in the way cognitive impressions are supposed to be, and if the Stoic definition of the cognitive impression is correct, there is no cognition. Hence, if all knowledge depends on cognitions, as the Stoics claim, nothing at all can be known. The Academics also offered a corollary to this argument, drawing on the Stoic principle of rationality mentioned above: