Ο επιβάτης δίπλα μου κοιμάται ήδη στο κάθισμά του.

Ο is the masculine singular definite article, meaning the.

So:

• ο = the for a masculine singular noun in the nominative
• επιβάτης = passenger

Together, Ο επιβάτης means the passenger.

Greek articles change for gender, number, and case, unlike English the, which always stays the same.

επιβάτης is in the nominative singular, because it is the subject of the sentence: the person doing the action.

In this sentence, the passenger is the one who is sleeping, so Greek uses the nominative form:

• ο επιβάτης = the passenger as subject

You might later see other forms of the same noun in other cases, but here nominative is the normal form because it is the subject.

δίπλα means next to / beside, and it is commonly followed directly by a weak pronoun like μου.

So:

• δίπλα μου = next to me / beside me
• δίπλα σου = next to you
• δίπλα του = next to him / next to it
• δίπλα της = next to her / next to it
• δίπλα μας = next to us

Greek often uses this structure very naturally without needing an extra word corresponding exactly to English to.

Yes. μου is a weak pronoun that can mean either:

• me / to me
• my

Its exact meaning depends on the structure.

Here:

• δίπλα μου = next to me

But in another phrase:

• το βιβλίο μου = my book

So the same form μου is used in more than one way. This is very common in Greek.

κοιμάται is the standard 3rd person singular form meaning he/she sleeps or is sleeping.

So:

• κοιμάμαι = I sleep / I am sleeping
• κοιμάται = he/she sleeps / is sleeping

This verb belongs to a group of verbs that look like middle/passive forms, even though the meaning is active in English.

You may sometimes hear other forms in everyday speech with related verbs, but κοιμάται is the normal standard form here.

That is a very common question.

In Greek, some verbs have forms that come from the middle/passive-type endings, but their meaning is not passive in English. κοιμάμαι is one of them.

So although κοιμάται may look passive to a learner, it simply means:

• he/she sleeps
• he/she is sleeping

It does not mean is being slept or anything passive like that.

This is just something to get used to with certain Greek verbs.

ήδη means already.

So:

• κοιμάται ήδη = is already sleeping

It shows that the action has already begun.

Its position is flexible, but here it comes naturally after the verb:

• Ο επιβάτης δίπλα μου κοιμάται ήδη...

That sounds very normal in Greek.

στο is a contraction of:

• σε + το = στο

Here, σε means in / at / on, depending on context, and το is the neuter singular article the.

So:

• στο κάθισμά του = literally in/on his seat

In English we usually say in his seat or in his chair/seat, but Greek uses σε + article here.

That happens because the noun is in a different case.

The basic form is:

• το κάθισμα = the seat

But after σε (here contracted as στο), Greek normally uses the accusative:

• το κάθισμα → το κάθισμα in the article+noun phrase, but when followed by a weak possessive pronoun, the stress is often shown as:
• το κάθισμά του = his seat

The accent in κάθισμά helps show the correct pronunciation when the possessive pronoun follows.

So this is mainly about pronunciation/stress in the phrase:

• κάθισμά του = his seat

Yes. Here του means his.

So:

• στο κάθισμά του = in his seat

Greek usually expresses possession with these weak pronouns after the noun:

• το βιβλίο μου = my book
• το βιβλίο σου = your book
• το βιβλίο του = his book
• το βιβλίο της = her book

So instead of putting a separate word before the noun like English his seat, Greek often says literally the seat his.

In this sentence, yes, the natural interpretation is that του refers back to ο επιβάτης.

So the meaning is:

• The passenger next to me is already sleeping in his seat.

Greek often uses these weak possessive pronouns when the owner is understood from context.

Because Greek verbs already include the person and number in their endings.

κοιμάται by itself already means:

• he/she sleeps
• he/she is sleeping

So Greek does not need a separate word like English is here.

This is very common in Greek. A single verb form often corresponds to an English subject + auxiliary + verb.

Yes.

Greek present tense can mean both:

• a general present: sleeps
• an action happening now: is sleeping

So κοιμάται can mean either, depending on context.

Because of ήδη and the situation described, the natural meaning here is:

• is already sleeping

That is, the passenger has fallen asleep and is asleep now.

Yes, Greek often allows flexible word order, and subjects can sometimes be omitted or moved.

For example:

• Δίπλα μου κοιμάται ήδη ο επιβάτης.
• Ο επιβάτης δίπλα μου κοιμάται ήδη στο κάθισμά του.

But the original sentence is clear and neutral. It introduces the subject first, which is often easiest for learners to understand.

Greek word order is more flexible than English, but different orders can slightly change emphasis.

Yes. κάθισμα is a normal and common word for seat.

It can be used for:

• a seat on a plane
• a seat on a bus
• a seat in a theater
• a chair seat, depending on context

So in this sentence, στο κάθισμά του naturally means in his seat.

Yes. In English, both are good translations.

• δίπλα μου = next to me
• δίπλα μου = beside me

Next to me is probably the most direct and common translation, but beside me is also correct.