Δεν ήξερα ποιο φλιτζάνι να πάρω, κι έτσι πήρα το μπλε.

Ήξερα is the imperfect of ξέρω.

Greek uses the imperfect for a past state or ongoing situation, and not knowing is a state. So Δεν ήξερα means I didn’t know / I wasn’t sure.

That is more natural here than a completed-event past form, because the sentence is describing your state of uncertainty before you chose the cup.

A useful point: Greek does not really use an aorist of ξέρω with the same meaning as English knew. If you want a completed idea like I found out / I learned, Greek often uses έμαθα instead.

Greek often leaves out the subject pronoun when it is clear from the verb ending.

• ήξερα = I knew
• πήρα = I took

So the I is already built into the verb form. You could add εγώ, but that would usually add emphasis or contrast:

• Εγώ δεν ήξερα... = I didn’t know... / As for me, I didn’t know...

Without εγώ, the sentence is neutral and natural.

Because φλιτζάνι is a neuter singular noun.

The question word ποιος / ποια / ποιο must agree with the noun in gender, number, and case:

• ποιος άντρας = which man
• ποια γυναίκα = which woman
• ποιο φλιτζάνι = which cup

So ποιο is used because φλιτζάνι is neuter.

This is a very common Greek structure.

English says:

• I didn’t know which cup to take

Greek does not have an infinitive like English to take in this kind of sentence, so it uses:

• να + verb

So:

• ποιο φλιτζάνι να πάρω = literally something like which cup that I take
• natural English: which cup to take

This pattern is very common after expressions like:

• δεν ξέρω τι να κάνω = I don’t know what to do
• δεν ήξερα πού να πάω = I didn’t know where to go
• σκέφτομαι τι να φορέσω = I’m thinking about what to wear

Because να πάρω is the aorist subjunctive, and it refers to one complete action: taking one cup.

Here, you are talking about a single choice and a single act, so the aorist is the natural form.

• να πάρω = to take, in the sense of one complete action
• να παίρνω = to be taking / to take repeatedly / habitually

In this sentence, να παίρνω would sound wrong or at least unnatural, because you are not talking about repeated or ongoing taking. You are talking about one decision.

Because παίρνω has an irregular aorist stem.

Its main forms are:

• παίρνω = I take
• να πάρω = that I take / to take
• πήρα = I took

So the present stem is παιρν-, but the aorist stem is παρ- / πάρ-.

This is very normal in Greek. Many common verbs change stem in the aorist.

So even though παίρνω, πάρω, and πήρα look different, they all belong to the same verb.

Κι έτσι means and so, so, or as a result.

The word κι is just a shortened form of και. It is very common, especially before a vowel, and it sounds natural in everyday Greek.

So these are both possible:

• κι έτσι
• και έτσι

But κι έτσι is especially common and smooth here.

In this sentence, it links the two ideas clearly:

• I didn’t know which cup to take,
• so I took the blue one.

Πήρα is the aorist of παίρνω, and it is used because the action is a single completed event in the past.

You made a choice and took the cup. That happened once and is finished, so the aorist is exactly the right tense.

• πήρα = I took

If Greek used an imperfect here, it would suggest repeated action or an ongoing background situation, which is not what this sentence means.

Because Greek can use the article + adjective/color to stand in for a noun that is understood from context.

Earlier in the sentence, the noun φλιτζάνι has already been mentioned. So in the second clause, Greek does not need to repeat it:

• το μπλε = the blue one
• literally: the blue

What is really understood is:

• το μπλε φλιτζάνι = the blue cup

English often uses one in this situation. Greek usually does not need a separate word for one here.

Because it stands for το μπλε φλιτζάνι, and φλιτζάνι is neuter singular.

So the article must also be neuter singular:

• το μπλε

If the hidden noun were masculine or feminine, the article would change:

• ο μπλε = the blue one, masculine
• η μπλε = the blue one, feminine
• το μπλε = the blue one, neuter

Here it is neuter because φλιτζάνι is neuter.

Usually μπλε is treated as indeclinable, which means it often stays the same form regardless of gender, number, or case.

So you can get patterns like:

• ο μπλε φάκελος = the blue envelope
• η μπλε τσάντα = the blue bag
• το μπλε φλιτζάνι = the blue cup
• τα μπλε ποτήρια = the blue glasses

The article and noun show the grammar, while μπλε itself usually stays the same.

That is why το μπλε is perfectly normal.

Greek uses different negative words depending on the verb form.

• δεν is used with indicative verbs
• μη(ν) is used with subjunctive, imperatives, and some non-indicative structures

In this sentence:

• Δεν ήξερα uses δεν because ήξερα is an indicative past form.

But if you wanted to negate the να clause, you would use μην:

• Δεν ήξερα ποιο φλιτζάνι να μην πάρω = I didn’t know which cup not to take

So the sentence shows both an actual example of δεν, and a context where μην would appear if that second part were negative.