1911 Encyclopedia Britannica
(Lat. "from a stronger [reason]"), a term used of an argument which justifies a statement not itself specifically demonstrated by reference to a proved conclusion which includes it; thus, if A is proved less than B, and is known to be greater than C, it follows a fortiori that C is less than B without further proof. The argument is frequently based merely on a comparison of probabilities (cf. Matt. vi. 30), when it constitutes an appeal to common sense.
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Chisholm, Hugh, General Editor. Entry for 'A Fortiori'. 1911 Encyclopedia Britanica. https://www.studylight.org/encyclopedias/eng/bri/a/a-fortiori.html. 1910.