I have read multiple questions on this site on Latin plurals, and I’ve learned that you can use both English plurals and Latin plurals with words which originate from Latin (e.g. referendum - referenda/​referendums). I however have a somewhat different question:

An example - When reading a text full of fallacies, like for example the argument from ignorance - argumentum ad ignorantiam, you often need to use plural forms to show that a text is ridden with them. How do you pluralize these types of Latin “word groups”?

If I extrapolate the rules which I have read from the other questions on the site, it would be (taking the argument from ignorance for example) both argumentum ad ignorantiams (or something similar) and argumenta ad ignorantias (argumentum is neutral, so the plural is argumenta, and ignorantiam is feminine accusative because of the preposition ad, so it becomes feminine accusative plural which is -as). However, the first form just seems totally wrong. Is this still legitimate? Or would the only option in these cases be correct Latin plurals?

P.S. I know you all probably think “why don’t you just say arguments from ignorance”, but I feel this could come in useful in other cases, for example in legal terminology.

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    The plural of any neuter Latin noun (including the ones that end in -um) is the same noun stem ending in -a. This is true whether it's subject or object; neuter nouns don't distinguish. So Argumenta. Nothing else has to be changed, since they're just prepositional phrases and don't have to agree in number with anything. Commented Jan 1, 2013 at 22:10
  • epicure.demon.co.uk/latinlesson.html
    – MetaEd
    Commented Jan 1, 2013 at 22:10
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    @JohnLawler: Exactly. Note that some neuter plurals end on -ia. Commented Jan 1, 2013 at 22:24
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    Personally, If I had to use the Latin, I would go with "arguments ad ignorantiams". Using Latin only really flies when you are using stock phrases, or if you are well schooled in Latin, writing to those well schooled in Latin (not very likely these days). Otherwise, it is the very definition of pretentious.
    – Lucas
    Commented Jan 2, 2013 at 3:22
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    @Lucas, please take a look at tchrist's first comment to my answer---"arguments ad ignorantiams" makes no more sense than "mothers-in-laws" or "courts martials." If you want to go down that route, it has to be "arguments ad ignorantiam" as suggested by Mitch in his answer. Commented Jan 2, 2013 at 14:23

4 Answers 4


If you want to go by the Latin, argumentum ad ignorantiam pluralises as argumenta ad ignorantiam (arguments to ignorance), and similarly reductio ad absurdum pluralises as reductiones ad absurdum (reductions to absurdity) – the point is that ad ignorantiam and ad absurdum (and, for that matter, the principii in petitio principii) serve as adjectival phrases, and are thus indeclinable in Latin.

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    This is correct, and I highly recommend using the Latin plurals with these Latin terms; if you're afraid of Latin, you can always revert to "argument from ignorance". Commented Jan 1, 2013 at 22:23
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    I don’t know why anyone would ever want to inflect each separate word in the phrase instead of the head noun only. After all, we don’t talk about mothers-in-laws nor ladies-in-waitings. Even an amicus curiae becomes several amici curiae, not amicus curiarum. And don’t get be started on casus belli.
    – tchrist
    Commented Jan 1, 2013 at 22:27
  • So this is correct Latin grammar. What is accepted practice in English?
    – Mitch
    Commented Jan 1, 2013 at 22:43
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    Either use the Latin plural, or try to treat the whole phrase as a unit and apply the regular English pluralisation. Whilst the English plural is sometimes preferable (e.g., octopuses instead of octopodes), the Latin plural is probably the less clunky option here. Commented Jan 1, 2013 at 22:57
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    It should probably be mentioned that if your Latin borrowing isn't a noun or nominal phrase in Latin (e.g., non sequitur), then you must use the English pluralisation. Commented Jan 1, 2013 at 23:14

The short answer is

ad hominem arguments


arguments ad hominem


argumenta ad hominem

in that order of popularity, because there are no stated rules.

To explain, first the Latin.

The plural of the stand alone 'argumentum' in English follows that in Latin:


The plural of 'argumentum ad ...' in Latin is

argumenta ad ...

the noun is properly (for Latin) the thing pluralized.

Now let's turn to English. A foreign phrase is often declined by the borrowers in the know exactly as in the original language. Depending on the language, the later users of the phrase may or may not be proficient in the grammar of the original, and usually it gets analyzed in as natural way as possible in English.

The plural of 'argumentum' alone given in dictionaries is the same as in Latin, namely:


That is for the word by itself.

In this example 'argumentum' is easily recognizable in English as 'argument', so the phrase is often given in mixed English/Latin as 'argument ad hominem' or 'an ad hominem argument'. There the plural is given as expected only affecting the noun:

ad ... arguments


arguments ad ...

or the proper Latin way

argumenta ad ...

the English/Latin mix becoming more popular recently for ad hominem and ad populum.

Also, sometimes the qualifier is given as the name of the argument type, e.g. "He used an ad hominem against me", and so there the plural is given as:

ad hominems

but again a plural only ever seems to have appeared for 'ad hominem'. but this never seems to appear ever in a plural form like 'argumentum ad hominems' (pluralizing the entire Latin phrase as though it were a single thing).

The latter support for the plural is only an argument de facto (by the questionable ngrams) rather than de jure, since dictionaries and style guides seem not to consider the possibility.

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    When you apply Occam’s Defacto-Knife™, you find that the opposite of du jour is really du soir. :)
    – tchrist
    Commented Jan 2, 2013 at 3:53

I wouldn’t try. You can instead say, if you must, 'The text contains many instances of argumentum ad ignorantiam.'

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    And why not, O down-voter? Commented Jan 4, 2013 at 18:39

To say "argumentum ad ignorantiams" doesn't work at all. It's the argument that needs to be plural. You can't add "s" to a foreign phrase like that to form a plural (although I expect someone will come up with an example to contradict me!). When it's a foreign word rather than a phrase, there's no ambiguity, so you could probably get away with it. (Though I'm not sure if referendum is a good example: many people choose "referendums" because "referenda" isn't necessarily a good Latin plural.)

So when it's a phrase, I'd say you should form the Latin plural correctly for the entire phrase. If you can't expect your audience to cope with that, then you should probably be avoiding the Latin altogether.

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    "You can't add 's' to a foreign phrase like that". Proof of this bald assertion, please.
    – Colin Fine
    Commented Jan 2, 2013 at 0:27
  • @ColinFine - Pedantry aside, do you disagree with me? In my answer, I make it clear that I'm open to the possibility that there may be examples where it might work (perhaps with phrases that are well-known enough to be a bit less foreign?). So far I've been unable to come up with an example myself that works well in English. Commented Jan 2, 2013 at 6:54
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    Not only can you, but sometimes you have no choice but to, because something that isn't a noun or nominal phrase in the source language, tautologically, has no meaningful plural as a noun or nominal phrase in the source language. For example, the plural of "non sequitur" and even of the absolutely ubiquitous noun "exit" must be "non sequiturs" and "exits" respectively, for the naive, would-be Latin plurals (viz, the third-person plural of those Latin verbal phrases) "non sequuntur" and "exeunt" mean "they don't follow" and "they leave," respectively. Commented Jan 2, 2013 at 15:03
  • Exit is by now a good English word. Non sequitur is a good example though. Perhaps we could argue that it has also become English; that the English "non sequitur" is actually the noun that the Latin "non sequitur' implies? Somehow, this makes me want to hyphenate it: non-sequitur, but perhaps that introduces other weirdnesses. Commented Jan 2, 2013 at 16:36
  • @Dominic, Your "doesn't work" is a wholly subjective judgment, which others might not share. I would probably not use the Latin tag at all, and if I did I would be showing off and probably would use a Latin plural; but others might well use the form you say doesn't work. You seem to be implying that it's in some way ambiguous, but I don't see it.
    – Colin Fine
    Commented Jan 3, 2013 at 0:11

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