n. (Logic) 1. a relation that holds of an ordered pair of elements, 〈x, y〉 if and only if a given relation holds of the ordered pair 〈y, x〉; that is, x has the converse relation to y if and only if y has the given relation to x. For example, on the domain of males, father of is the converse of son of. The converse of a given relation Rxy is often written Ryx.
2a. in Aristotelian logic, a proposition derived from another by interchanging its subject and predicate terms. Thus, for example, all men are liars can be derived from all liars are men; this, however, is clearly not a valid form of argument.
b. analogously, a conditional statement derived from another by interchanging antecedent and consequent, such as
if John missed the meeting, then his train was late
from
if John's train was late, then he missed the meeting.
This is not a valid form of argument unless if is taken to represent the biconditional.