A fortiori argument

The Latin phrase argumentum a fortiori literally means one of the following: It denotes a proof of a claim by means of an already proved stronger claim. Example: If it is forbidden to ride a bike with an extra passenger, then it is also forbidden to ride a bike with two extra passengers.
 * "from the stronger"
 * "even more so"
 * "with even stronger reason"

There are two types of the a fortiori argument:
 * a maiore ad minus: from bigger to smaller
 * a minore ad maius: from smaller to bigger

The a fortiori argument is most often used in order to reinforce a claim, though sometimes also to incorrectly justify a claim taking it as a premise (petitio principii).