Learn English – Plural of “camera obscura”

In most languages indefinite articles stem from that language's word for one. For instance in French un, or in German ein, In Italian and Spanish uno or in Portuguese um.

English is no exception: an was derived from one. Note that an was the original indefinite article; the shorter a came later when the final "n" was dropped before consonants.

In some of the languages I mentioned above, the plural form of the indefinite articles is simply formed by applying the noun plural inflection: unos/unas or uns/umas.

In others, such as German and Italian, there is no plural form to the indefinite article. Italian use the partitive article degli/delle as a substitute and this is probably also the origin of the French plural form des.

For some reason English did not go through this last step either. To understand why we need to go back to the way Old English solved the problem.

In Old English adjectives have a different declension depending on whether the noun they qualify is determined or not.

"The glad man" reads

se glæd guma

whereas, "a happy man" is:

glæda guma

As one can see, only the adjective changes.
For one given adjective, you could therefore have different inflections depending on:
- the noun gender (masculine, feminine, neuter)
- the noun being singular or plural
- the four cases (nominative, accusative, genitive, dative)
- whether the reference is definite or indefinite.
So that the same adjective would have to follow either the "definite" declension or one of three "indefinite" declensions.

þa glædan guman

Edit
<conjecture>
The theory I'm trying to check (community please feel free to edit) is that in various languages (Icelandic for a language very close to Old English or Romanian) the article is added as a suffix to the noun. Then it often "detaches" and passes in front of the noun. Icelandic is half way through for the definite article in that matter.

As for the Old English indefinite article, my conjecture is that the process never went through for a number of possible reasons:
- The "loss of inflection" of early Middle English won the race
- The plural of "an" was not easy to evolve at that time (the Romance "-s" plural had not imposed itself yet).
</conjecture>

But the need is still there, just as in any other language where a specific word emerged for the plural indefinite article. This gap is filled by placeholders such as some or a number of.

Most linguist agree that Proto Indo European did not use articles. Latin does not have any kind of article, and Ancient Greek arguably had no indefinite article either - it was using something very much like present-day English some (τις - "a certain"). And I believe that Old German did not have any article either.

It is a very remarkable fact that articles appeared in many modern Indo European languages in a largely mutually independent yet very similar manner. My feeling is that their emergence compensates for the gradual loss of inflection in these languages. But then present-day German is a powerful counterexample...

The answer is, unsatisfyingly, that it depends. Most native speakers aren't fluent in the borrowed language and so won't know the grammar principles there.

Sometimes things are borrowed exactly, like Latin sayings, and stand alone with no possibility of declining, like 'ceteris paribus'

Sometimes a simple thing, like a plural, if easy, is declined, like Greek the singular for criteria is usually said 'criterion'. But sometimes that strict adherence to a foreign grammar is lost and 'criteria' is used for singular, 'criterias' for plural.

Depending on how unnatural or infrequent the foreign word is, the foreign manner may be preserved or not: 'My fiancée' for a female to be married is correct English not because English has grammatical gender like French but English allows an alternate lexical item (ignoring for the moment that it is a difference in spelling only). But 'The banana was flambé' is grating in English, so 'flambéd' is preferred, despite it sounding very unFrench.

The principle is that someone who has heard the foreign word repeats it to an English speaker. However clear that foreign word is spoken (by native speaker or not), the English speaker will assimilate it as best they can, ignoring what just doesn't work in English, and preserving possibly what does work.

So, for an arbitrary foreign word slipped into English, what form should it take? You probably want to preserve what you can and drop what just sounds bad. And then English speakers will do with it what they may. Early on, 'data' was plural, but nowadays, since 'datum' is almost entirely unheard of, different groups continue to use 'data' as plural (rarer) and others use it as a mass noun (taking a singular verb).

So there's no hard and fast rule; try to conjugate as much as you can, but once it is firmly in English, then English rules will apply.