converse
The conditional you get by swapping the if-part and the then-part.
The converse of "if P, then Q" is "if Q, then P." A conditional and its converse can differ in truth value, so assuming one because the other is true is a mistake.
Examples
The converse of "if it is a dog, then it is a mammal" is "if it is a mammal, then it is a dog," which is false.
See also