Learn Hardcore Greek: Ο κοινός μας φίλος, που είναι μέλος στην ίδια ομάδα, συχνά μοιράζεται μαζί μας αστεία βίντεο. - Our mutual friend, who is a member of the same group, often shares funny videos with us.

Ο κοινός μας φίλος = the mutual friend of ours → this assumes both speakers know which friend we’re talking about (a specific, identified person).
Ένας κοινός μας φίλος = a mutual friend of ours → this would introduce some mutual friend that hasn’t been specified before.

In the sentence, we are clearly talking about a specific, known mutual friend, so ο is the natural choice.

What exactly does κοινός mean here, and why is it before μας?

Κοινός means common / mutual / shared. So ο κοινός μας φίλος literally means the mutual friend of ours → our mutual friend.

About the order:

ο κοινός μας φίλος = the usual, natural word order.
μας is an unstressed possessive pronoun (our). In Greek, it normally comes after the noun (or after the adjective that comes before the noun), not before it like in English.

Some patterns:

ο φίλος μας = our friend
ο καλός μας φίλος = our good friend
ο κοινός μας φίλος = our mutual friend

So κοινός comes before μας, and both together describe φίλος.

Could we also say ο φίλος μας ο κοινός instead of ο κοινός μας φίλος?

You can say ο φίλος μας ο κοινός, but:

It sounds more marked, a bit more stylistic or emphatic.
It’s less common in everyday speech than ο κοινός μας φίλος.

In everyday modern Greek, ο κοινός μας φίλος is the standard, neutral way to say our mutual friend. Use ο φίλος μας ο κοινός only if you want a slightly more dramatic or literary feel.

Why is που used for “who” in που είναι μέλος… and not something like ο οποίος?

In modern Greek, που is the normal, everyday relative pronoun used for:

who
that
which

So:

ο φίλος μας, που είναι μέλος… = our friend, who is a member…

Ο οποίος / η οποία / το οποίο is more formal or written-style and often sounds heavier or more official in speech:

ο φίλος μας, ο οποίος είναι μέλος… → correct, but more formal.

For ordinary conversation or neutral writing, που is by far the most common choice.

Why is there a comma before που: Ο κοινός μας φίλος, που είναι μέλος...?

The comma shows that που είναι μέλος στην ίδια ομάδα is non‑restrictive (extra information, not essential to identify which friend).

With the comma:
Ο κοινός μας φίλος, που είναι μέλος στην ίδια ομάδα, …
= Our mutual friend, who is a member of the same group, …
→ There is only one such mutual friend in the context; we’re just adding a detail about him.

If we dropped the comma:

Ο κοινός μας φίλος που είναι μέλος στην ίδια ομάδα…
→ This would sound like you are distinguishing the mutual friend who is a member of the same group from other mutual friends who are not.

So the comma indicates “extra, descriptive information”, just like in English.

In που είναι μέλος στην ίδια ομάδα, why do we say στην and not just σε?

Στην is simply σε + την contracted:

σε = in / at / into / to
την ίδια ομάδα = the same group (feminine, singular, accusative)
σε + την → στην

So:

σε την ίδια ομάδα → spoken and written as στην ίδια ομάδα

Grammatically, you could also express membership with a genitive:

είναι μέλος της ίδιας ομάδας = he is a member of the same group

Both:

είναι μέλος στην ίδια ομάδα
είναι μέλος της ίδιας ομάδας

are correct. Using σε / στην is very common and a bit more colloquial; using της sounds a bit more formal or written.

Why is ίδια feminine here in στην ίδια ομάδα?

In Greek, adjectives agree in gender, number, and case with the noun they describe.

ομάδα (group) is feminine, singular, accusative.
So ίδιος (same) must also be feminine, singular, accusative → ίδια.

That’s why we have:

η ίδια ομάδα (nominative)
την ίδια ομάδα (accusative, after σε/στην)

So στην ίδια ομάδα is grammatically:
σε + την (fem. acc.) + ίδια (fem. acc.) + ομάδα (fem. acc.).

What’s going on with the verb μοιράζεται? Why not μοιράζει?

Μοιράζεται is the middle / reflexive form of the verb μοιράζω:

μοιράζω = I share / distribute (something) – active voice
μοιράζομαι = I share (something) [with others], I share for myself / among us – middle/reflexive

In the sentence:

συχνά μοιράζεται μαζί μας αστεία βίντεο
= he often shares funny videos with us

Using μοιράζεται is very natural here, because we’re thinking of sharing with others (a reciprocal, social action), which Greek tends to express with μοιράζομαι.

Μοιράζει would sound more like “he distributes/dispenses funny videos” (too literal or mechanical) and is less natural in this context.

Could we change the position of συχνά? For example, say μοιράζεται συχνά instead of συχνά μοιράζεται?

Yes. In Greek, adverbs like συχνά (often) can move around fairly freely:

συχνά μοιράζεται μαζί μας αστεία βίντεο
μοιράζεται συχνά μαζί μας αστεία βίντεο
μοιράζεται μαζί μας συχνά αστεία βίντεο

All are grammatically correct and natural. The differences are minor and mostly about rhythm or slight emphasis:

Συχνά μοιράζεται… → a tiny emphasis on how often this happens.
Μοιράζεται συχνά… → a bit more neutral ordering.
…μαζί μας συχνά… → slight emphasis on “it’s with us that he often does this.”

In ordinary speech, all three would sound fine.

Why μαζί μας and not με εμάς?

Both exist, but they are not the same:

μαζί μας = together with us / with us (in the sense of company, participation)
με εμάς (or με μας) = with us in a broader sense (could be company, but also means “on our side”, “using us”, etc.)

In this sentence:

μοιράζεται μαζί μας αστεία βίντεο
= he shares funny videos with us (we are the people he shares them with)

Μαζί μας is the standard, idiomatic way to express “with us” in the sense of sharing, being together in an activity.

You could say:

μοιράζεται με εμάς αστεία βίντεο

It’s still grammatical, but μαζί μας sounds more natural and conversational here.

Why is there no article before αστεία βίντεο? Why not τα αστεία βίντεο?

In Greek, the definite article is used only when you mean specific, known things.

αστεία βίντεο = funny videos (some, in general – indefinite)
τα αστεία βίντεο = the funny videos (specific ones, known from context)

In this sentence, we are not talking about some already identified set of videos; we mean funny videos in general that he happens to share. So no article is natural.

Greek often drops the article with plural indefinite objects, where English uses “some” or just plural without article:

αγοράζω βιβλία = I buy books (some books)
στέλνει μηνύματα = he sends messages
μοιράζεται αστεία βίντεο = he shares funny videos

Why is αστεία in the neuter plural form here?

Because:

βίντεο is a neuter noun in Greek.
It’s also indeclinable (the form βίντεο stays the same in singular and plural).
In the sentence, αστεία βίντεο is the direct object (accusative plural).

Adjectives must agree with the noun:

Gender: neuter
Number: plural
Case: accusative (same form as nominative in neuter plural)

So αστείος (funny) becomes:

αστεία βίντεο = funny videos (neuter plural)

Some forms:

αστείος φίλος (masc. sg.)
αστεία φίλη (fem. sg.)
αστείο βίντεο (neut. sg.)
αστεία βίντεο (neut. pl.)

The αστεία in the sentence is this neuter plural form.

Why is the verb in the present tense (μοιράζεται) if we mean “often shares”?

In Greek, the present tense (imperfective aspect) is used for:

habits
repeated actions
general truths

So:

συχνά μοιράζεται μαζί μας αστεία βίντεο
= he often shares funny videos with us
(a repeated, habitual action)

You don’t need a special tense for “habitual present” as in some languages; the normal present with an adverb like συχνά (often) is enough to convey that idea.