In short

Greek “a/an” is ένας for masculine nouns, μία (usually written μια) for feminine, ένα for neuter. It agrees with its noun in gender and case, exactly like the definite article, and in the accusative the masculine becomes έναν.

Two things surprise English speakers. First, there is no plural of the indefinite article: where English says “some books”, Greek simply drops the article and says βιβλία. Second, Greek uses no article at all in a predicate that names a profession, a nationality, a religion or a role after είμαι and γίνομαι: Είμαι δάσκαλος, not Είμαι ένας δάσκαλος.

The rule

1. Agreement. ένας/μία/ένα stands in front of the noun and takes the gender and the case of that noun: ένας φοιτητής (subject), έναν φοιτητή (object), μία ερώτηση, ένα παιδί. The genitive forms ενός/μιας/ενός exist and you will meet them, but at A1 you only need to recognise them; the genitive gets its own lesson later.

2. First mention against known mention. ένας/μία/ένα introduces something into the conversation for the first time; once it is known, the definite article takes over:

• Ένας άντρας μπήκε στο μαγαζί. → Ο άντρας ζήτησε καφέ.
• Ένας φίλος μου δουλεύει εκεί. → Ο φίλος μου δουλεύει εκεί. (a friend of mine → my friend, someone you already know about)

3. No plural indefinite article. ένας/μία/ένα is singular only. English “some books”, “flowers”, “friends of mine” is expressed by the bare noun in the plural:

• Αγόρασα βιβλία. — I bought (some) books.
• Στο τραπέζι υπάρχουν λουλούδια. — There are flowers on the table.

Writing ένα βιβλία is a grammatical error, not a stylistic one: a singular article cannot stand in front of a plural noun.

4. No article in predicate nouns. After είμαι (“be”) and γίνομαι (“become”), a noun that classifies the subject — a job, a nationality, a religion, a role, a family relation — appears bare, with neither the definite nor the indefinite article:

• Είμαι δάσκαλος. — I am a teacher.
• Ο Νίκος είναι φοιτητής. — Nikos is a student.
• Η Άννα είναι Ελληνίδα. — Anna is Greek.
• Θέλω να γίνω γιατρός. — I want to become a doctor.

English forces “a” here; Greek leaves it out. Think of the bare noun as an adjective-like label rather than as a countable thing.

Forms & patterns

The indefinite article, all cases. It has no vocative (you do not call out to “a man”) and, crucially, no plural at all.

μια and μία are the same word: μια is the everyday one-syllable pronunciation (one syllable, therefore no accent), μία is the two-syllable form, used when you want to stress “one”. The same holds for μιας / μίας.

The article with a noun, nominative and accusative:

Only the masculine changes shape between the two cases, and that is exactly why the -ν of έναν matters: it is the one signal that tells έναν φίλο (masculine object) apart from a neuter ένα.

Singular against plural — the article simply disappears:

Examples

Common mistakes

• Είμαι ένας δάσκαλος. -> Είμαι δάσκαλος. — after είμαι a noun of profession takes no article; English “a” has no equivalent here.
• Η Άννα είναι μία Ελληνίδα. -> Η Άννα είναι Ελληνίδα. — the same rule covers nationality, religion and role.
• Θέλω να γίνω ένας γιατρός. -> Θέλω να γίνω γιατρός. — γίνομαι behaves exactly like είμαι.
• Αγόρασα ένα βιβλία. -> Αγόρασα βιβλία. — there is no plural indefinite article; a singular article cannot stand before a plural noun.
• Είδα ένα άντρα. -> Είδα έναν άντρα. — masculine accusative singular is έναν; ένα would make it look neuter.
• Έχω ένα ερώτηση. -> Έχω μία ερώτηση. — η ερώτηση is feminine, so the article must be feminine too.
• Ένας φίλος μου ήρθε χθες. Ένας φίλος μου έφερε δώρο. -> Ένας φίλος μου ήρθε χθες. Ο φίλος μου έφερε δώρο. — the second mention is already known, so it goes definite.

Tips

• Learn the article together with the noun as one block: ένας φοιτητής, μια φίλη, ένα παιδί. The article is your fastest reminder of the gender.
• Keep the -ν of έναν in every position. Unlike την, which drops it before most consonants, the masculine τον and έναν always hold on to it, because it is the only thing distinguishing masculine from neuter.
• When you want to say “some” in the plural, say nothing: μόνο το ουσιαστικό. If you feel the urge to translate “some” word by word, that is the moment to leave it out.
• Before answering “What do you do?”, rehearse the bare pattern: Είμαι μηχανικός. Είμαι φοιτήτρια. Είμαι μαθήτρια. No article, ever.
• The bare predicate rule bends once the noun carries a descriptive adjective: Είμαι δάσκαλος, but Είναι ένας εξαιρετικός δάσκαλος (“he is an outstanding teacher”), where ένας adds a note of appraisal rather than counting.
• Remember the second accent when a weak possessive follows a word stressed on its third syllable from the end: ένας δάσκαλός μου, ένα μάθημά μας.
• ένας/μία/ένα is also the number “one”. Context decides; when you really mean the quantity, stress it in speech and use the full μία.