Πριν κοιμηθώ, αλλάζω την παλιά παπλωματοθήκη, γιατί ήταν βρόμικη.

Because after πριν in this kind of sentence, Greek often uses the subjunctive, and here the verb is in the aorist subjunctive:

• κοιμηθώ = I sleep / I go to sleep / I fall asleep in a subjunctive form
• κοιμάμαι = I am sleeping / I sleep as the normal present form

So:

• Πριν κοιμηθώ = before I go to sleep / before I fall asleep

The aorist here does not mean past time. It shows the action as a single whole event: the moment of going to sleep.

In Modern Greek, πριν can be followed directly by a subjunctive form, especially in common everyday language.

So this is normal:

• Πριν κοιμηθώ

You may also encounter:

• Πριν να κοιμηθώ

But in many contexts, especially natural speech, πριν + subjunctive without να is very common.

Αλλάζω is present tense because the sentence describes a habit or a repeated action:

• Πριν κοιμηθώ, αλλάζω... = Before I go to sleep, I change...

Greek often uses the present tense for routines and general habits, just like English can say:

• Before I go to bed, I change the old duvet cover.

So this is not necessarily happening right now one single time; it can describe what the speaker normally does.

Because this is the direct object of αλλάζω.

Breakdown:

• την = the for a feminine singular accusative noun
• παλιά = old, matching the feminine singular accusative noun
• παπλωματοθήκη = duvet cover, also feminine singular accusative here

So the whole phrase means:

• την παλιά παπλωματοθήκη = the old duvet cover

The verb αλλάζω takes a direct object, so the noun goes in the accusative.

Παπλωματοθήκη means duvet cover.

It is a compound word:

• πάπλωμα = duvet / quilt
• θήκη = case / cover

So literally it is something like cover for a duvet.

It is a useful example of how Greek often builds long nouns by combining smaller words.

Because it describes παπλωματοθήκη, which is a feminine noun.

So the adjective has to agree with the noun in:

• gender
• number
• case

Here:

• παπλωματοθήκη = feminine singular
• therefore βρόμικη = feminine singular

So:

• η βρόμικη παπλωματοθήκη = the dirty duvet cover
• την παλιά παπλωματοθήκη, γιατί ήταν βρόμικη = the old duvet cover, because it was dirty

Even though βρόμικη comes later in the sentence, it still refers back to παπλωματοθήκη.

Because βρόμικη describes one feminine singular thing: the duvet cover.

Compare:

• βρόμικος = masculine singular
• βρόμικη = feminine singular
• βρόμικο = neuter singular
• βρόμικα = plural or sometimes neuter plural/adverbial use depending on context

Since παπλωματοθήκη is feminine singular, the correct form is:

• ήταν βρόμικη = it was dirty

Because the speaker is giving the reason for changing it:

• γιατί ήταν βρόμικη = because it was dirty

The idea is that the duvet cover was in a dirty state, and that is why the speaker changes it.

ήταν is the imperfect of είμαι (to be). Here it gives background information: the cover was dirty.

The same word, γιατί, can mean both:

• because
• why

Context tells you which meaning it has.

In this sentence:

• ..., γιατί ήταν βρόμικη.

it clearly means because, since it introduces a reason.

Compare:

• Γιατί αλλάζεις την παπλωματοθήκη; = Why are you changing the duvet cover?
• Την αλλάζω γιατί ήταν βρόμικη. = I’m changing it because it was dirty.

So learners must rely on context and sentence structure.

Because Greek usually does not need subject pronouns when the verb ending already shows the person.

For example:

• αλλάζω = I change
• κοιμηθώ = I go to sleep / I fall asleep

So εγώ (I) is unnecessary unless the speaker wants emphasis or contrast.

For example:

• Εγώ αλλάζω την παλιά παπλωματοθήκη, όχι εσύ.
• I’m the one who changes the old duvet cover, not you.

Without that kind of emphasis, Greek normally leaves the pronoun out.

In Greek, adjectives can come before or after the noun, but before the noun is very common, especially in ordinary description.

So:

• την παλιά παπλωματοθήκη = the normal, neutral way to say the old duvet cover

You may also see:

• την παπλωματοθήκη την παλιά
• την παπλωματοθήκη την παλιά

but those patterns usually sound more marked, emphatic, or stylistically different.

For a learner, the safest default is:

• article + adjective + noun

when giving a simple description.

In natural English, the best translation is usually:

• before I go to sleep or
• before I fall asleep

Because κοιμηθώ is an aorist subjunctive, it points to the action as a whole event, not the ongoing state of sleeping.

So the phrase is closer to:

• before I get to sleep / before I fall asleep

than to the general idea of before I sleep.

Because Πριν κοιμηθώ is an introductory subordinate clause:

• Πριν κοιμηθώ, αλλάζω...

Greek often separates such opening clauses with a comma, much like English does:

• Before I go to sleep, I change...

There is also a comma before γιατί, separating the main statement from the reason clause:

• ..., γιατί ήταν βρόμικη.

So the punctuation here helps show the sentence structure clearly.

Yes. Βρόμικη is perfectly natural and means dirty / filthy in a general sense.

But Greek also has related words, for example:

• λερωμένη = stained / soiled / dirty
• βρόμικη = dirty, often more general or stronger

So ήταν βρόμικη is very normal, but in some contexts a speaker might choose another adjective depending on the type of dirtiness they want to express.

It can feel like either, depending on context.

With objects like clothes, sheets, pillowcases, or a duvet cover, αλλάζω often means:

• change
• replace with a clean one

So here the natural meaning is something like:

• I change the old duvet cover
• I replace the old duvet cover

Greek uses αλλάζω very broadly in situations where English might say change, switch, or replace.