Are the terms a fortiori, a priori, and a posteriori bad Latin? If so, how and when did they become established?

I understand that the dative case never takes a preposition in Latin—a most welcome clue in a language where the dative and ablative have opposite meanings but often identical form. But fortiori appears to be unambiguously dative, yet introduced by a preposition. And yet the meaning appears to be ablative: "with stronger reason" ("all the more so" more colloquially in English). The stronger reason is the source of the conclusion being justified. And how would you fill in the elided noun: a fortiori rationi or a fortiore ratione? I don't see how the dative could even make sense here. Nothing is being given to the stronger reason and there’s no suggestion that the stronger reason has anything at stake in the matter. Weight is coming from the stronger reason, as suggested by the preposition a (short for ab as in ablative!).

  • To anyone looking at William Whitaker's Words: I just checked another couple sources online, and it appears that, in this case, it's wrong.
    – anon
    Feb 24, 2016 at 13:13
  • @QPaysTaxes: What do you mean by that? Is Words a book?
    – Cerberus
    Feb 24, 2016 at 16:17
  • @Cerberus It's an online dictionary that's popular, at least in my school. I was about to use it as a source but decided to double-check with another one and it was wrong, so I figured it would be worth making a note.
    – anon
    Feb 24, 2016 at 16:23

2 Answers 2


In classical Latin, the ablative of comparatives could end on -i, although -e is probably more common. Here are a few quotations that I think must be conceded to contain ablatives:

Cornelius Nepos, Vitae Ca. 2.2.2:

… ibi cum diutius moraretur, P. Scipio Africanus consul iterum, cuius in priori consulatu quaestor fuerat, uoluit eum de prouincia depellere …

L. Iunius Moderatus Columella, De Re Rustica

… de cuius cultu dicturos nos priori uolumine polliciti iam nunc disseremus.

Titus Livius, Ab Urbe Condita

… et ceteri in suas quisque prouincias profecti, et quibus prorogatum imperium erat easdem quas priori anno regiones obtinuerunt.

Titus Livius, Periochae Librorum A. U. C. 56.15:

… delatus est ultro Scipioni Africano a senatu populoque R. consulatus; quem cum illi capere ob lege, quae vetabat quemquam iterum consulem fieri, non liceret, sicut priori consulatu legibus solutus est.

Publius Ovidius Naso, Metamorphoses 8.443:

Toxea, quid faciat, dubium pariterque volentem
ulcisci fratrem fraternaque fata timentem
haud patitur dubitare diu calidumque priori
caede recalfecit consorti sanguine telum.

"Still warm from its prior carnage".

  • Fantastic!! How did you find these?
    – Ben Kovitz
    Feb 24, 2016 at 23:06
  • 1
    @BenKovitz: I just searched a Latin corpus, this time that of the Hewlett–Packard foundation (or what is it?): latin.packhum.org/search?q=priori%23 The hash signifies a word boundary. There are better corpora, such as the Bibliotheca Teubneriana Latina, but that isn't available online, and I don't have it installed at the moment.
    – Cerberus
    Feb 24, 2016 at 23:31

My impression is that fortiori, priori and posteriori are ablative forms, but they have been declined badly — from the classical point of view.

Making this mistake is quite easy. Both -e and -ī appear as singular ablative endings in the third declensions. For adjectives, -ī is always used in positive (ie. neither comparative nor superlative) and -e always in comparative. Therefore it is no surprise if by (false) analogy the ablative ending -ī makes it to the comparative as well.

As you explain in your question, ablative makes semantically much more sense than dative. And of course it fits better with the preposition.

From a classical point of view the expressions you mention are bad Latin. I suspect that such declensions may have been canonical in some form of medieval Latin, but I am not an expert in such medieval developments. It seems most natural that this misdeclension is a part of a more wide-spread slip from classical standards, not a stand-alone mistake.

  • 5
    It's not medieval Latin, it's still Classical. Pliny the Elder wrote 'a priori parte' in his Naturalis Historia. But you're otherwise correct about the shift.
    – cmw
    Feb 24, 2016 at 13:39
  • @C.M.Weimer, thanks! I didn't know it was already a classical phenomenon.
    – Joonas Ilmavirta
    Feb 24, 2016 at 13:45
  • @C.M.Weimer Mehercule! Why does Pliny use both forms? Or is that a transcription error?
    – Ben Kovitz
    Feb 24, 2016 at 13:58
  • 1
    @BenKovitz As Joonas mentioned, the -ī is for adjectives. Pars would never have an -ī for its ablative.
    – cmw
    Feb 24, 2016 at 14:05
  • @C.M.Weimer Just to be sure I understand, do you mean that Pliny made a mistake, or that the -ī/-e convention is not as clear-cut as suggested by grammatical tables?
    – Ben Kovitz
    Feb 24, 2016 at 23:08

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