Κοιμάμαι καλύτερα όταν το δωμάτιο είναι ήσυχο.

Κοιμάμαι is the normal modern Greek verb for I sleep.

It looks like a middle/passive form because it ends in -μαι, but for this verb that is simply the standard present-tense form. In other words, you should learn κοιμάμαι as the basic dictionary form meaning to sleep.

Some present-tense forms are:

• κοιμάμαι = I sleep / I am sleeping
• κοιμάσαι = you sleep
• κοιμάται = he/she/it sleeps
• κοιμόμαστε = we sleep
• κοιμάστε = you (plural) sleep
• κοιμούνται / κοιμούνται = they sleep

So even though it looks passive to an English speaker, here it is just the ordinary verb meaning sleep.

Greek usually omits subject pronouns when they are not needed, because the verb ending already shows the subject.

• κοιμάμαι already means I sleep
• so εγώ is often unnecessary

You would add εγώ only for emphasis or contrast:

• Εγώ κοιμάμαι καλύτερα... = I sleep better...
  • maybe contrasting with someone else

In a neutral sentence, Κοιμάμαι καλύτερα... is more natural.

καλύτερα means better.

Here it is an adverb, because it modifies the verb κοιμάμαι:

• Κοιμάμαι καλύτερα = I sleep better

Compare:

• καλός = good
• καλύτερος / καλύτερη / καλύτερο = better, as an adjective
• καλά = well
• καλύτερα = better, as an adverb

So:

• ένα καλύτερο δωμάτιο = a better room
• κοιμάμαι καλύτερα = I sleep better

όταν can mean when or whenever, depending on context.

In this sentence:

• Κοιμάμαι καλύτερα όταν το δωμάτιο είναι ήσυχο.

it most naturally means when / whenever the room is quiet.

Because the main verb is in the present and expresses a general truth or habitual situation, English often translates it as:

• I sleep better when the room is quiet
• or I sleep better whenever the room is quiet

So όταν introduces a time clause.

Because the sentence describes a general, repeated situation.

• όταν το δωμάτιο είναι ήσυχο = when the room is quiet

Greek commonly uses the present indicative in clauses like this when talking about things that are generally true or habitual.

So the structure is:

• Κοιμάμαι καλύτερα = I sleep better
• όταν το δωμάτιο είναι ήσυχο = when the room is quiet

This is very natural Greek for a general statement.

το δωμάτιο is in the nominative case because it is the subject of είναι.

Breakdown:

• το = the
• δωμάτιο = room

In the clause:

• το δωμάτιο είναι ήσυχο
• the room is quiet

the room is the thing being described, so it is the subject.

Also, δωμάτιο is a neuter noun, which matters for the adjective too.

Because ήσυχο has to agree with το δωμάτιο, and δωμάτιο is neuter singular.

Greek adjectives change form to match the noun in gender, number, and case.

For ήσυχος = quiet, the forms are:

• ήσυχος = masculine
• ήσυχη = feminine
• ήσυχο = neuter

So:

• ο άντρας είναι ήσυχος = the man is quiet
• η γυναίκα είναι ήσυχη = the woman is quiet
• το δωμάτιο είναι ήσυχο = the room is quiet

Not in this sentence.

You need ήσυχο because it is an adjective describing το δωμάτιο:

• το δωμάτιο είναι ήσυχο = the room is quiet

ήσυχα is usually an adverb meaning quietly:

• Μιλάει ήσυχα. = He/She speaks quietly.

So:

• ήσυχο = quiet, describing a neuter noun
• ήσυχα = quietly, describing how an action happens

The basic order here is very natural:

• Κοιμάμαι καλύτερα όταν το δωμάτιο είναι ήσυχο.

Greek word order is often more flexible than English, because endings show grammatical roles more clearly. So you can sometimes move elements for emphasis.

For example:

• Όταν το δωμάτιο είναι ήσυχο, κοιμάμαι καλύτερα.

This means the same thing, but now the when-clause comes first.

You could also stress καλύτερα or another part depending on context, but the original order is the most straightforward and neutral.

It can mean either, depending on context.

Greek present tense often covers both:

• I sleep (habitual)
• I am sleeping (right now)

In this sentence, because of καλύτερα and the general meaning of the clause, it is understood as a habitual/general statement:

• I sleep better when the room is quiet

If you wanted a clearly ongoing meaning, context would usually make that obvious.

Literally, το δωμάτιο means the room, so it can sound specific. But in everyday Greek, this can still be used in a fairly general sense depending on context.

Here it most naturally means something like:

• when the room is quiet
• often understood as when my/the room I’m in is quiet

If you wanted to speak more generally about rooms in general, you might say something else, but this sentence sounds very natural for ordinary speech.

A rough pronunciation guide is:

Kyoi-MA-me ka-LI-te-ra O-tan to tho-MA-tio EE-ne EE-si-ho

A few notes:

• οι in Κοιμάμαι sounds like ee
• δ in δωμάτιο is like th in this
• αι in είναι sounds like e
• χ in ήσυχο is a throaty sound, like the ch in German Bach or Scottish loch

The stress falls on:

• κοιΜΑμαι
• καΛΥτερα
• δωΜΑτιο
• ΕΙναι
• Ησυχο

Not if you want the same meaning.

• όταν = when / whenever
• αν = if

So:

• Κοιμάμαι καλύτερα όταν το δωμάτιο είναι ήσυχο. = I sleep better when the room is quiet.

But:

• Κοιμάμαι καλύτερα αν το δωμάτιο είναι ήσυχο. = I sleep better if the room is quiet.

That second sentence is also possible, but it sounds a bit more conditional. The original sentence with όταν sounds more like a general pattern or regular fact.