The term 'a fortiori' is Latin for 'from the stronger.' It indicates that some fact naturally proves some other fact by a stronger argument or reason than any other fact. Although the term is used to show that there is a stronger argument for something, the Latin word for "argument" is omitted because it is understood that the term refers to an argument or reason.

Argument from stronger reason: Joe isn't old enough to get married; therefore, Joe isn't old enough to get divorced.

A fortiori is a legal term meaning " for a stronger (reason)," that is, more logically compelling.

From the stronger = Ex fortioribus

a fortiori