Ο φίλος μου είναι πολύ ομιλητικός όταν πίνει καφέ.

Ο is the masculine singular definite article, meaning the.

So:

• ο φίλος = the friend

In Greek, the definite article is used very often, including in places where English might sometimes leave it out. Here it simply marks friend as a specific person.

Because φίλος is masculine singular nominative, the article must also be ο.

In Greek, unstressed possessive words like μου (my) usually come after the noun:

• ο φίλος μου = my friend
• literally: the friend my

This is completely normal Greek word order.

A native English speaker often expects the possessive to come before the noun, but Greek commonly places these short possessive forms after it.

Greek often keeps the definite article even when English uses a possessive:

• ο φίλος μου = my friend
• η αδερφή μου = my sister
• το σπίτι μου = my house

So although English does not say the my friend, Greek normally does use the article here.

Sometimes Greek can drop the article in certain contexts, but ο φίλος μου is the standard, neutral form.

Yes. είναι is the verb to be in the third person singular:

• είμαι = I am
• είσαι = you are
• είναι = he/she/it is

So:

• Ο φίλος μου είναι πολύ ομιλητικός = My friend is very talkative

Greek often does require the verb to be in sentences like this, just as English does.

Yes. ομιλητικός is an adjective, and Greek adjectives change to match the noun in gender, number, and case.

Here it describes ο φίλος:

• φίλος is masculine singular nominative
• so the adjective is also ομιλητικός (masculine singular nominative)

Other forms would be:

• ομιλητικός = masculine
• ομιλητική = feminine
• ομιλητικό = neuter

For example:

• Ο φίλος είναι ομιλητικός.
• Η φίλη είναι ομιλητική.
• Το παιδί είναι ομιλητικό.

Here πολύ means very. It modifies the adjective ομιλητικός:

• πολύ ομιλητικός = very talkative

This is a common use of πολύ as an adverb.

A learner may notice that πολύς / πολλή / πολύ can also mean much / many, but in this sentence πολύ is the indeclinable adverb very, not the adjective many/much.

όταν means when. In Greek, when you talk about something that happens regularly or generally, όταν is commonly followed by the present tense:

• όταν πίνει καφέ = when he drinks coffee

This does not have to mean right now. It can describe a habitual situation:

• whenever he drinks coffee
• when he drinks coffee in general

So Greek uses the present tense here naturally.

The subject is understood from the context and from the verb form.

• πίνει = he/she/it drinks

Since the earlier subject is ο φίλος μου, Greek naturally understands that the same person is the one drinking coffee.

Greek often omits subject pronouns when they are not needed. This is very common.

So Greek does not need to say he explicitly here. The meaning is:

• My friend is very talkative when he drinks coffee.

πίνει is the third person singular present tense of πίνω (to drink).

Basic forms:

• πίνω = I drink
• πίνεις = you drink
• πίνει = he/she/it drinks

So here:

• όταν πίνει καφέ = when he drinks coffee

Greek often leaves out the article with substances or general objects when speaking in a broad, non-specific way.

So:

• πίνει καφέ = he drinks coffee

This is similar to English, where we also usually say drink coffee, not drink the coffee, unless we mean a specific coffee.

If you wanted to refer to a specific coffee, the article could appear:

• πίνει τον καφέ του = he drinks his coffee
• πίνει τον καφέ = he drinks the coffee

But in your sentence, καφέ is general, so no article is needed.

Yes, Greek word order is more flexible than English, but the version here is the most neutral and natural.

The structure is:

• Ο φίλος μου = subject
• είναι = verb
• πολύ ομιλητικός = complement
• όταν πίνει καφέ = time clause

Greek could rearrange parts for emphasis, for example:

• Όταν πίνει καφέ, ο φίλος μου είναι πολύ ομιλητικός.

That means essentially the same thing, but puts more focus on the when he drinks coffee part.

So the given order is standard, but not the only possible one.

Yes, ομιλητικός is a normal adjective meaning talkative or chatty.

Depending on context, Greek speakers might also use other expressions, such as:

• πολυλογάς = very talkative / someone who talks a lot
• λαλίστατος = very talkative, rather strong or expressive
• μιλάει πολύ = he talks a lot

But ομιλητικός is a straightforward and correct adjective for this sentence.

Greek uses an accent mark to show the stressed syllable in most words.

Examples here:

• φίλος → stress on φί-
• πολύ → stress on -λύ
• ομιλητικός → stress on -κός
• πίνει → stress on πί-
• καφέ → stress on -φέ

These accents are important in writing because they tell you where the word stress goes. Stress is a regular and meaningful part of Greek pronunciation.

You would change the words that agree with the noun’s gender:

• Η φίλη μου είναι πολύ ομιλητική όταν πίνει καφέ.

Changes:

• Ο → Η
• φίλος → φίλη
• ομιλητικός → ομιλητική

The verb είναι stays the same, and πίνει καφέ also stays the same.

Yes. In a sentence like this, όταν can naturally be understood as:

• when
• whenever

Because the clause uses the present tense and describes a typical pattern, many English speakers would interpret it as:

• My friend is very talkative whenever he drinks coffee.

So the Greek is slightly broader than a one-time event unless the context makes it specific.