Learn Hardcore Greek: Έχουμε έναν κοινό φίλο που μένει στην ίδια γειτονιά. - We have a mutual friend who lives in the same neighborhood.

Έχουμε is 1st person plural: we have.
You can say Εμείς έχουμε έναν κοινό φίλο…, but Έχουμε έναν κοινό φίλο… is more natural in everyday speech.

So “we” is understood from the form of the verb έχουμε.

Why is it έναν and not ένα?

Greek has gender and case:

φίλος (friend) is masculine.
In this sentence, friend is the direct object (we have a friend), so it’s in the accusative case: φίλο.

The indefinite article “a” must match in gender and case:

masculine accusative: έναν
neuter accusative: ένα
feminine accusative: μία / μια

So you say:

έναν φίλο (a male friend)
μία φίλη (a female friend)
ένα παιδί (a child)

Here: έναν κοινό φίλο = a mutual friend (masc. acc. sing. across the phrase).

Why is it φίλο and not φίλος?

φίλος is the nominative form (used mainly for the subject of the sentence):

Ο φίλος μένει εδώ. = The friend lives here.

In our sentence, friend is the object of the verb have (we have a friend), so it goes into the accusative:

nominative: ο φίλος (subject)
accusative: τον φίλο (object)

With the article and adjective:

ο κοινός φίλος = the common friend (subject)
έναν κοινό φίλο = a common friend (object)

So φίλο is correct because it’s in the accusative case.

What exactly does κοινός / κοινό mean here? Is it “same” or “mutual”?

κοινός has a range of meanings:

common, shared, mutual
also “ordinary, not special” in other contexts

In έναν κοινό φίλο, it specifically means:

a friend that two (or more) people share
→ a mutual friend / a friend in common.

It is not the same as ίδιος (same) in this context:

έχουμε τον ίδιο φίλο = we have the same friend (could mean we are both talking about the same person, often with some previous context)
έχουμε έναν κοινό φίλο = we don’t necessarily know who we’re talking about yet, just that there exists one mutual friend between us.

In practice, έναν κοινό φίλο is exactly how you say a mutual friend.

Why is it κοινό and not κοινός?

Adjectives in Greek agree with the noun in:

gender
number
case

The noun here is φίλο:

masculine
singular
accusative

The adjective κοινός must match this:

nominative masculine singular: κοινός
accusative masculine singular: κοινό

So:

ο κοινός φίλος (subject)
έναν κοινό φίλο (object)

That’s why it’s κοινό in this sentence.

What does που mean here? Is it the same as the question word “who”?

In this sentence, που is a relative pronoun, not a question word. It means:

who, that, or which (depending on context in English)

So:

…έναν κοινό φίλο που μένει…
= …a mutual friend who lives…

It’s similar to English who/that in “the friend who lives nearby”.

Note: Greek also has ο οποίος / η οποία / το οποίο etc. as more formal relative pronouns, but in everyday speech που is by far the most common.

Why is it μένει and not ζει? Don’t both mean “live”?

Both verbs can be translated as live, but they are used differently:

μένω = to live, to reside, to stay (somewhere)
- Μένω στην Αθήνα. = I live in Athens.
ζω = to live, to be alive, to experience life
- Ζω μια ήσυχη ζωή. = I live a quiet life.
- Ευτυχώς, ζει ακόμα. = Fortunately, he/she is still alive.

In που μένει στην ίδια γειτονιά, we are talking about where the friend resides, so μένει is the natural choice.

που ζει στην ίδια γειτονιά would sound a bit more literary or marked here, and less typical in everyday speech about address/residence.

What tense are Έχουμε and μένει?

Both are in the present simple (ενεστώτας):

Έχουμε = we have
μένει = he/she lives

In Greek, the present tense covers:

actions happening right now:
- Τώρα μένει εδώ. = He is now living here.
habits or general facts:
- Μένει στην Αθήνα. = He lives in Athens (as a general fact).

So Έχουμε έναν κοινό φίλο που μένει στην ίδια γειτονιά naturally means We have a mutual friend who lives in the same neighborhood (as a general, current fact).

What is στην exactly? Why not just σε?

στην is a contraction:

σε (in / at / to) + την (the – feminine accusative singular)
= στην

So:

στην ίδια γειτονιά = in the same neighborhood

Patterns:

σε + τον → στον (to the / in the, masculine)
σε + την → στην (feminine)
σε + το → στο (neuter)

You could write it separately (σε την ίδια γειτονιά), but in standard modern Greek it’s almost always written in the contracted form στην.

Why is it ίδια γειτονιά and not ίδιο γειτονιά?

Again, agreement of adjective and noun:

γειτονιά is feminine, singular, accusative.
So the adjective ίδιος (same) must match:
- masculine acc. sg.: ίδιο (for neuter) / ίδιον (ancient) – but modern:
  - masc acc. sg.: ίδιον (rare) / mostly ίδιο in everyday? Actually:
    Modern patterns:
  - masc nom: ίδιος, acc: ίδιο (same form as neuter).
  - fem nom/acc: ίδια
  - neut nom/acc: ίδιο
For our purposes:
- feminine accusative singular: ίδια

So:

στην ίδια γειτονιά = in the same neighborhood (correct)
στην ίδιο γειτονιά is wrong, because ίδιο doesn’t match the feminine noun γειτονιά.

Why is στην ίδια γειτονιά also in the accusative case?

Because in modern Greek, the preposition σε (in, at, to) normally takes the accusative case.

σε + την ίδια γειτονιά → στην ίδια γειτονιά (feminine accusative)

Similarly:

στον φίλο = to the friend (masculine accusative)
στο σπίτι = in/to the house (neuter accusative)

So the whole phrase στην ίδια γειτονιά is in accusative due to the preposition σε.

Can I change the word order, like in English? For example, put που μένει at the end?

You have some flexibility, but not complete freedom.

These are natural:

Έχουμε έναν κοινό φίλο που μένει στην ίδια γειτονιά.
Έχουμε έναν φίλο, έναν κοινό φίλο, που μένει στην ίδια γειτονιά. (with a slight pause/emphasis)
Έχουμε έναν κοινό φίλο, που μένει στην ίδια γειτονιά. (comma adds a slight extra comment feel)

These are not natural or sound odd:

✗ Έχουμε έναν φίλο κοινό που μένει στην ίδια γειτονιά. (the position of κοινό is strange)
✗ Έχουμε έναν κοινό φίλο στην ίδια γειτονιά που μένει. (splitting που μένει like this is unnatural)

Basic rule for you at this level:
→ Keep που + verb right after the noun it describes:

έναν κοινό φίλο [που μένει…]
= a mutual friend who lives…

How would I say “We have the same friend who lives in the same neighborhood”? Is that different from this sentence?

Yes, slightly different nuance.

Your original sentence:

Έχουμε έναν κοινό φίλο που μένει στην ίδια γειτονιά.
= We have a mutual friend who lives in the same neighborhood.
(We share a friend; we’re introducing that information.)

To say “the same friend”, you’d normally use τον ίδιο φίλο:

Έχουμε τον ίδιο φίλο, που μένει στην ίδια γειτονιά.
= We have the same friend, who lives in the same neighborhood.

Difference in feel:

έναν κοινό φίλο – introduces the idea of a mutual friend (indefinite, one of possibly many).
τον ίδιο φίλο – points to a specific, already-identified friend who is the same person for both speakers.