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

This says that you ought to believe the consequences of your beliefs regardless of how implausible these are. This can have bizarre implications.

Suppose that you affirm A but deny its consequence B. Since you hold A, and A entails B, you ought to accept B. But since you hold not-B, and not-B entails not-A, you ought to accept not-A. So this principle absurdly tells you to accept the opposite of both of your beliefs!