The conversion of logical statements can be "simple" or "per accidens" (restricting). The simple converse of "No A is B" is "No B is A," and that of "Some A is B" is "Some B is A." The "per accidens" converse of "All A is B" is "Some B is A."
There is no converse for statements of the type "Some A is not B." For example, from the fact some humans are not male, we can't conclude some males are not human. Generally, the converse of a true statement need not be true and the converse of a false statement need not be false.
The concept of "converse" is used in the study of logic.
The first recorded use of "converse" to mean "reversed" occurred in Sir Richard Joseph Sullivan's travel book "A View of Nature" from 1794. But the first recorded mathematical usage dates to Sir Henry Billingsley's 1570 translation of Euclid.
Beware of the mistake of arguing from a particular principle (such as "it is acceptable to lie to save someone's life") to a general case (such as "it is acceptable to lie"). This is called the "converse fallacy of the accident" or "converse accident."