Conveying all the more so; with an even greater or stronger reason: Literally, a fortiori means from the stronger point and it is used to introduce a statement that, assuming a previous statement is accepted as true, must be all the more true.

If statement "A" is true, then a fortiori statement "B" must be true; for example, if students can't or won't do twenty minutes of homework each night, then a fortiori, they can't or won't do sixty minutes each night.