Why do we use indefinite articles?

Question

I was elementary school student

vs

I was an elementary school student.

Why is the first sentence incorrect? And why do we need that "an"??

Answer 1

The sentence

*I was elementary school student

is ungrammatical because it violates this rule:

• Predicate nouns that are count nouns [like student] require an indefinite article
  (predicate nouns that are mass nouns [like rice] do not).

As for an, that is required (instead of a) when it comes before the vowel /ɛ/
at the beginning of elementary. The rule is:

• Use a /ə/ before spoken consonants,
  and use an /ən/ before spoken vowels
  (spelling doesn't count; only pronunciation).

Answer 2

Some languages have articles and others do not. This and other differences between languages illustrate how their development (what I might call 'glossogenesis') must be subject to the random dictates of evolution. For example, Ancient Latin has no articles at all; the same applied to the slavic language, Russian. English, as well as German from which it is derived, has both a definite article (the/der) and an indefinite article (*a/*ein). Ancient Greek had a definite article (ho - ο) but no indefinite article, but the modern Greeks also have an indefinite article (ena - ενα).

The Mediterranean Latin countries have languages derived from Latin, which are similar but not the same as French. So Italian uses il and Spanish uses el when the French use le. All three probably derive from the Latin for that, ille. So the populations of first Italy, then France (Gallia), then Spain came to speak the Latin of Rome, no doubt with their own regional variants, and then, with the fall of Rome, these descendent languages grew apart again.

Greek, on the other hand, spoken throughout the Levant remained much the same till the fall of Constantinople in CE 1204. Under he Ottoman empire, outside the monasteries, the Greek language gradually became a kind of 'Yiddish' mixture of Greek and Turkish, called demotic. But in this case, because the Greeks obtained their freedom from the Ottoman by revolt over a long period, the proponents of Greek culture artificially tried to restore the original 'pure' Greek language, called catharevousa (pure). Even this did not work entirely, and modern Greek today is a kind of compromise without some of the more rarified features removed. But even now, Greek for a cup is flytzani - φλυτζανι from Turkish fincan; spice is bachari from Turkish baharat; grocer is manavis - μαναβης; a bag is tsanta - τσαντα from canta, words all too embedded in life, shopping and cooking to ripped out and replaced for the sake of an ethnic ideology.

Along the Levant coast in the middle ages, the polyglot nature of the city populations led to the emergence of a mixture of Italian, French, Greek, Arabic and Spanish, known as Lingua Franca - the Frankish Language. It made it possible for the speakers for all these different languages to trade and negotiate together.

So how languages develop in the first place and change over time is a function of a variety of circumstance and proximity. The English did not learn their language from Germans, or from the Anglo-Saxons. After the Romans left Britain, various waves of Anglo-Saxons came over from Northern Germany, from Denmark and from what is now Holland and settle here, bringing their Germanic languages (with their similarities and differences), and settled. The English to a large extent are the descendants of the Anglo-Saxons. That is why most of everyday English is germanic: hand (hand), house (haus), garden (garten), dream (traum), street (straße = strasse)...

So both the similarities and the differences between languages are a function of the connection and the separation, respectively, of the people who speak them. The Russians get along fine without articles, except when they are trying to use languages that have them. Most Greeks today would be surprised at how many turkish words remain in their language.