{ 1 } - If A and B are inconsistent, then if you accept A then you ought not to accept B.
{ 2 } - If A and B are inconsistent, then you ought not to combine accepting A with accepting B.
{ 3 } - Both mean the same thing.

This formula can have bizarre implications. Suppose that A and B are inconsistent and yet you hold both. Since you hold A, and A is inconsistent with B, you ought not to accept B. And since you hold B, and B is inconsistent with A, you ought not to accept A. So the principle absurdly tells you to give up both beliefs!