Is there a difference in meaning between argumentum ad and argumentum a? Does the latter even have authoritative usage in Latin?*

Here are some samples that I've found, not always from authoritative works, which seem to follow an interesting pattern:

  • argumentum ad misericordiam: an appeal to mercy or pity, attempting to override the law or truth

  • argumentum ad hominem: an appeal specific to the person you're trying to persuade, i.e. telling each person a different story, hoping to get them all on your side; or, in contemporary usage, trying to get the faults of a person who advocates an idea to rub off onto the idea

  • argumentum ad populum: an appeal to the people at large, i.e. arguing that the idea is popular, not that it's true (or perhaps arguing that since it's popular, it's likely true)

  • argumentum ad baculum: an appeal to force ("the stick"), i.e. convincing by threat rather than by enlightening

  • argumentum ad verecundiam: an appeal to reverence; I once read verecundia explained as the kind of bashfulness that you feel in the presence of something great or socially important, so that appealing to this emotion works like this: "How could say such an awful thing about our church?"

  • argumentum a simili: an appeal to similarity: since this is similar to that, the rule for that applies to this

  • argumentum a contrario (or e contrario): an appeal to the contrary: since this is different from that, the rule for that doesn't apply

  • argumentum a coherentia: an appeal to internal consistency: a proposal to resolve a conflict between rules that keeps the system of rules coherent

  • argumentum a fortiori [ratione?]: an appeal to a comparable, stronger case where the result is known

The pattern appears to be as follows:

  • Ad introduces something about who is judging the matter: their emotions, their loyalties, their numbers, their power or lack of it—all matters that are outside the matter under consideration.

  • Ab introduces something within the topic: a kind of fact, a relevant factor, a relation between the present case and a known or settled case.

Is this right? Is there an authoritative source about this? Or can you point to common usages of argumentum or ad/ab in other contexts that might serve as a precedent for the pattern above?


*Not just classical Latin.

Here are two apparent counterexamples that I think are not really counterexamples. I post them here to give people an opportunity to confirm or refute my understanding of them (I'll be grateful for either).

Argumentum ab auctoritate est fortissimum in lege.

One might say that an authority is outside the topic and therefore should follow the ad pattern. However, the authority is understood as the source of the law, not as a factor specific to the person being appealed to. Since the authority is the source of the law, it is properly the source of the decision when considered in connection with the facts of the case.

Perhaps we could understand all the argumenta ab as appeals whose source is the next thing mentioned. That naturally calls for the ablative case.

By that token, argumenta ad would be appeals that "target" something about the person being persuaded rather than "coming from" the topic.

Argumentum a maiore ad minus negative non valet; valet e converso.

This one has ad introducing a part of the topic, certainly nothing specific to the person being appealed to. However, I am thinking that this is still not a counterexample, because ad is serving a different meaning: it's paired with ab to indicate the direction of the reasoning: "from the greater to the lesser", i.e. which proposition is the premise and which is the conclusion.

  • 1
    I think your analysis makes sense, and it fits with the way I've always translated the two expressions—*argumentum ad* is "appeal to" and argumentum a is "argument [derived] from." The argumentum a cohærentia isn't really an appeal TO coherence, which is located in the listener—it's an appeal whose BAISIS IS (putative) coherence located in the argument. (Of course the baculum isn't located in the listener but it pertains more to the listener than to the argument!) – Joel Derfner Aug 12 '16 at 23:34
  • @JoelDerfner That's an interesting way to translate argumentum. I've never been sure whether to think of it as "appeal" or "argument"; apparently it really is both, with the preposition clarifying as needed. BTW, what led me to this question was finding that Wikipedia had renamed its article "A fortiori argument" to "Argumentum a fortiori", apparently by analogy with the argumentum ad phrases. Have you found the argumentum a phrases in actual use? – Ben Kovitz Aug 13 '16 at 19:00
  • I haven't, but I've also never read logic in Latin, so that's hardly a surprise. – Joel Derfner Aug 13 '16 at 19:17

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