If John who is 18 is not too young to go to war, then a fortiori 19 year-old Peter is not too young.
A fortiori
Definition
A Latin term meaning literally 'from [the] stronger'. Translated into English and used in the particular context of legal writing, the term often means 'from [the] stronger [argument]'. If a particular fact is true, then one can infer that a second fact is also true.
Definition from Nolo’s Plain-English Law Dictionary
(ah-for-shee-oh-ree) Latin for "with even stronger reason," which applies to a situation in which if one thing is true then it can be inferred that a second thing is even more certainly true. Thus, if one party is too young to serve as administrator, then his younger brother certainly is too young.
Definition provided by Nolo’s Plain-English Law Dictionary.
August 19, 2010, 5:10 pm
In the Supreme Court case Gail Atwater, et al., Petitioners v. City of Lago Vista et al., , Justice Souter quotes the case Holyday v. Oxenbridge from 1631 that uses the term a fortiori:
"In Holyday v. Oxenbridge, Cro. Car. 234, 79 Eng. Rep. 805 (K.B. 1631), the Court of King’s Bench held that even a private person (and thus a fortiori a peace officer) needed no warrant to arrest a “common cheater” whom he discovered “cozen[ing] with false dice.”
Using the example in Holyday, if it is true that any person can arrest a "common cheater". Then, of course we can safely infer that a police officer can arrest a "common cheater" because a police officer has even more of a right to arrest than an other person.
