Δεν καταλαβαίνω όλες τις λεπτομέρειες, αλλά θα ρωτήσω την καθηγήτρια.

not

Breakdown of Δεν καταλαβαίνω όλες τις λεπτομέρειες, αλλά θα ρωτήσω την καθηγήτρια.

• αλλά: but
• καταλαβαίνω: to understand
• θα: will

Questions & Answers about Δεν καταλαβαίνω όλες τις λεπτομέρειες, αλλά θα ρωτήσω την καθηγήτρια.

Where is the subject “I” in this sentence? Why is εγώ not written?

In Greek, the subject pronoun is usually dropped, because the verb ending already shows who the subject is.

• καταλαβαίνω = I understand
  The ending -ω tells us the subject is 1st person singular (I).

So:

• Δεν καταλαβαίνω όλες τις λεπτομέρειες = I don’t understand all the details
  even though εγώ is not written.

You can say:

• Εγώ δεν καταλαβαίνω όλες τις λεπτομέρειες…

but then you are emphasizing I (as in “I don’t understand all the details (maybe others do)”).

How does negation work here? Why is δεν before καταλαβαίνω?

Modern Greek uses the negative particle δεν (or δε in speech) directly before the verb.

• καταλαβαίνω = I understand
• δεν καταλαβαίνω = I do not understand

Basic rule:
> δεν + verb

Examples:

• Δεν τρώω. = I don’t eat.
• Δεν μιλάω ελληνικά. = I don’t speak Greek.

Before some consonants, especially π, τ, κ, ψ, ξ, people often drop the final -ν in everyday speech and writing: δε.
Here, δεν καταλαβαίνω is the standard, fully written form.