A fortiori. The argument à fortiori, from the stronger, consists in
inferring from the greater case to the less, e. g. inferring the
operation of a cause in a less difficult case from its operation in a
more difficult one, the superiority or inferiority of one thing to
another from its superiority or inferiority to that which is superior or
inferior to it, and the like.
It has been pronounced impossible to exhibit à fortiori reasoning in
regular syllogistic form, and such arguments have been even entitled
syllogisms without a middle term. I have however maintained, and
I venture to think proved the contrary.(1)
(1) Outline of Logic, 2nd ed. pp. 139-142.