How did Carneades respond to the claim that Academic skepticism is self-contradictory?

To address the claim that Academic skepticism is self-contradictory—specifically the argument that claiming "knowledge is impossible" is itself a knowledge claim—Carneades offered a subtle defense.1

He argued that Academic skepticism should not be viewed as a formal theory regarding the nature of knowledge or the world. Instead, he characterized it as an argumentative strategy. Under this approach, the skeptic does not attempt to prove the positive assertion that "nothing can be known". Rather, the skeptic assumes that knowledge is impossible and defends that assumption against the claims of others. By doing so, Carneades shifted the burden of proof onto those who assert that knowledge is possible, thereby avoiding the trap of making a self-refuting knowledge claim himself.1

Additionally, to address criticisms that his skepticism rendered human action impossible, Carneades proposed that "probability" (or "approvability") serves as a practical guide for daily life.2