definition of a fortiori:
(from Latin. translates to "with greater reason") a logical concept which allows for an assumption of fact, based on another independent conclusion or fact. In other words, because one fact is true, a fortiori lets us find that some other conclusion is also true.
a fortiori, as it might be used:
The attorney argued that if amnesia was insufficient to find the defendant incompetent to stand trial, a fortiori the lack of recall could not support a claim of incompetence.
a fortiori, in an example:
Because we know that Fergus has never been out of his home state of Florida, we can assume, a fortiori, that he has never lived in the state of Washington.