a fortiori

adv.
For a still stronger reason; all the more.

[Latin : ā, ab, from + fortiōrī, ablative of fortior, stronger.]

(a fort-tee-OR-ee)

adverb
For an even stronger reason; even more so.

Etymology
From Latin, literally from the stronger.

Usage
"'If your argument is good for this case, then your argument is a fortiori good for testing everyone in school,' Justice David H. Souter told Linda M. Meoli, the lawyer representing Independent School District No. 92 ..." — Linda Greenhouse; Supreme Court Seems Ready To Extend School Drug Tests; The New York Times; Mar 20, 2002.

"The Governor is a sailing man - indeed, when it comes to monetary waters, he is positively an old salt. He knows what it is to have shot in the locker, and, a fortiori (as it were), to have no shot in the locker." — William Keegan; In my View: George Calls the Shots in Clarke's Battle; The Guardian (London, UK): Feb 12, 1995.

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(Latin, from the stronger) Phrase used for ‘all the more’ or ‘even more so’: if all donkeys bray, then a fortiori all young donkeys bray.

This entry contains information applicable to United States law only.

[Latin, With stronger reason.] This phrase is used in logic to denote an argument to the effect that because one ascertained fact exists, therefore another which is included in it or analogous to it and is less improbable, unusual, or surprising must also exist.

All the more so, with greater reason