Learn Hardcore Greek: Χτες το βράδυ διάβαζα όταν με πήρες. - Last night I was reading when you called me.

διάβαζα is imperfective past (imperfect): an ongoing/background action, like English “I was reading.”
πήρες is perfective past (aorist): a single, complete event, like English “you called.” Together they mean: an ongoing action was in progress when a single event interrupted it.

Could I say διάβασα instead of διάβαζα here?

No. διάβασα (aorist) means “I read (and finished).” In this structure with όταν, it would sound odd or change the meaning to a completed reading event tied to that moment. To keep the sense “I was reading (at that moment),” you need the imperfective: διάβαζα.
If you want to say you read after the call, rephrase: Αφού με πήρες, διάβασα or Μετά που με πήρες, διάβασα.

Could I also say όταν με έπαιρνες?

με έπαιρνες (imperfect) can mean:

“while you were calling me” (simultaneous, ongoing), or
“whenever you used to call me” (habitual). It’s potentially ambiguous. For one specific call that interrupted your reading, όταν με πήρες (aorist) is the natural choice. For clear simultaneity of two ongoing actions, many speakers prefer καθώς or ενώ with the imperfect: Καθώς/Ενώ με έπαιρνες, διάβαζα.

Why is it με πήρες, not πήρες με?

Greek weak object pronouns (clitics) normally come before the finite verb:

με πήρες (you called me) They go after an affirmative imperative:
πάρε με (call me) With particles θα/να/ας, the clitic follows the particle and precedes the verb:
θα με πάρεις, να με πάρεις

Does με πήρες always mean “you called me”?

In phone-related contexts, yes, με πήρες is shorthand for με πήρες (τηλέφωνο) = “you called me.”
But παίρνω also means “take,” so in other contexts με πήρες can mean “you took me (with you).” If there’s any risk of confusion, say με πήρες τηλέφωνο or μου τηλεφώνησες.

What’s the difference between με πήρες (τηλέφωνο) and μου τηλεφώνησες?

Meaning: both mean “you called me.”
Grammar:

παίρνω (τηλέφωνο) takes a direct object in the accusative: με, σε, τον, την.
τηλεφωνώ takes an indirect object (typically a genitive clitic): μου, σου, του, or a σε + accusative phrase (e.g., τηλεφώνησα σε σένα).
Register: με πήρες is very common in everyday speech; μου τηλεφώνησες is a bit more neutral/formal. Note: με κάλεσες usually means “you invited me,” not “you phoned me.”

Do I need to include τηλέφωνο after με πήρες?

No. Με πήρες by itself is perfectly natural in conversation. Adding τηλέφωνο just makes it explicit: Με πήρες τηλέφωνο.

Why is there an article in το βράδυ? Can I say χτες βράδυ?

Time-of-day nouns usually take the definite article in adverbial expressions: το πρωί, το απόγευμα, το βράδυ.
You can also say χτες βράδυ (colloquial and very common). Both χτες το βράδυ and χτες βράδυ are fine.

Is χτες, χθες, or εχθές correct? How do you pronounce them?

All are correct:

χτες and χθες are the most common spellings; both are pronounced [xtes].
εχθές is a bit more formal/literary; pronounced [eˈxtes].
The letter χ is like the German “ch” in “Bach.” The cluster χθ is written but in Modern Greek it’s still pronounced [xt].

Should there be a comma before όταν?

Not when the όταν-clause comes after the main clause: Διάβαζα όταν με πήρες (no comma).
If you put the όταν-clause first, use a comma: Όταν με πήρες, διάβαζα.
An initial time phrase like Χτες το βράδυ may optionally be followed by a comma for readability: Χτες το βράδυ, διάβαζα όταν με πήρες.

Can I change the word order?

Yes, Greek word order is flexible. All of these are acceptable:

Χτες το βράδυ διάβαζα όταν με πήρες.
Διάβαζα χτες το βράδυ όταν με πήρες.
Όταν με πήρες, διάβαζα χτες το βράδυ. The choice affects emphasis/focus slightly but not the core meaning.

Does διαβάζω mean “to read” or “to study”?

Both. διαβάζω can mean “read” (a book, article) or “study” (do homework/revise). For “study at university,” Greek typically uses σπουδάζω.
Examples:

Διαβάζω ένα βιβλίο. (I’m reading a book.)
Διαβάζω για τις εξετάσεις. (I’m studying for the exams.)

Is it βράδυ or βράδι?

Both spellings exist. βράδυ is the standard/recommended spelling; βράδι is a recognized variant.

Why are there no subject pronouns (εγώ, εσύ)?

Greek is a pro‑drop language: the verb ending shows the subject. διάβαζα already means “I was reading,” πήρες means “you (sg.) called.”
Use subject pronouns for emphasis/contrast: Εγώ διάβαζα όταν εσύ με πήρες.

How would I express the same idea about the future? Is όταν θα με πάρεις correct?

Standard Greek avoids όταν θα…. Use the (perfective) non‑past after όταν and put θα in the main clause:

Όταν με πάρεις, θα διαβάζω. (When you call me, I’ll be reading.)
Όταν με πάρεις, θα διαβάσω. (When you call me, I’ll read/I’ll start reading.)
Choose θα διαβάζω for an ongoing future action; θα διαβάσω for a single, completed future action.

What are the past forms of παίρνω and διαβάζω relevant here?

παίρνω: aorist πήρα, πήρες, πήρε, πήραμε, πήρατε, πήραν; imperfect έπαιρνα, έπαιρνες, έπαιρνε, ἐπαίρναμε, ἐπαίρνατε, ἔπαιρναν.
διαβάζω: aorist διάβασα, διάβασες, διάβασε, διαβάσαμε, διαβάσατε, διάβασαν; imperfect διάβαζα, διάβαζες, διάβαζε, διαβάζαμε, διαβάζατε, διάβαζαν.
In the sentence you have the imperfect διάβαζα and the aorist πήρες.

If I want to say “I read after you called me,” how would I phrase it?

Use a connector that shows sequence:

Μετά που με πήρες, διάβασα.
Αφού με πήρες, διάβασα. For “as soon as,” you could say:
Μόλις με πήρες, άρχισα να διαβάζω.

Are there alternatives to όταν here, like ενώ, καθώς, or την ώρα που?

Yes, with slight nuances:

την ώρα που = “at the moment when”: Χτες το βράδυ διάβαζα την ώρα που με πήρες.
καθώς / ενώ emphasize simultaneity/contrast and usually pair with the imperfect for ongoing actions:
Χτες το βράδυ διάβαζα καθώς/ενώ με έπαιρνες. (while you were calling me)
Using καθώς/ενώ with aorist (πήρες) is uncommon because aorist denotes a point‑like event.

How do I make it polite/plural?

Change the verb to 2nd person plural and keep the clitic the same:

Χτες το βράδυ διάβαζα όταν με πήρατε. (you = plural or polite)