Learn Hardcore Greek: Αν το μέγεθος δεν είναι σωστό, θα τα επιστρέψω και θα τα ανταλλάξω με κάτι άλλο. - If the size isn't right, I will return them and exchange them for something else.

Its article is το (neuter singular nominative/accusative).
The adjective that describes it (σωστό) is also neuter singular, because adjectives agree in gender, number, and case with the noun they modify.

So:

το μέγεθος = the size (neuter singular)
σωστό = correct/right (neuter singular, to match μέγεθος)

That’s why we have το μέγεθος and σωστό, not η μέγεθος / σωστή or ο μέγεθος / σωστός.

Why is it δεν είναι σωστό and not δεν είναι σωστά?

The adjective refers to το μέγεθος (the size), which is singular, so the adjective must also be singular:

το μέγεθος δεν είναι σωστό = the size is not right (singular → σωστό).

Σωστά would be neuter plural, used for something like:

Τα νούμερα δεν είναι σωστά.
The numbers are not correct.

Here, we only talk about one size, so σωστό is singular.

Why do we use δεν and not μην here?

Greek has two main negation words: δεν and μη(ν).

δεν is used with finite verbs in the indicative mood, like normal statements:
- δεν είναι (is not)
- δεν έχω (I don’t have)
- δεν πάω (I don’t go)
μη(ν) is used mainly with:
- the subjunctive (να μην πάω, not to go)
- the imperative (μην πας!, don’t go!)
- and some other special constructions.

In δεν είναι σωστό, the verb είναι is in the present indicative, so we must use δεν, not μην.

Why does the “if” part use the present tense: Αν το μέγεθος δεν είναι σωστό and not αν το μέγεθος δεν θα είναι σωστό?

In Greek, when you talk about a future condition, you normally use:

Present tense in the if-clause
(Αν το μέγεθος δεν είναι σωστό…)
Future tense with θα in the result clause
(…θα τα επιστρέψω και θα τα ανταλλάξω…)

So the pattern is:

Αν
- present → θα
  - future

Using θα in the if-clause (αν το μέγεθος δεν θα είναι σωστό) is normally incorrect or at least very unnatural in standard Greek. That’s different from English, where learners often want to say “if it will be…”.

So:

Correct: Αν το μέγεθος δεν είναι σωστό, θα τα επιστρέψω.
Wrong / unnatural: Αν το μέγεθος δεν θα είναι σωστό, θα τα επιστρέψω.

What does τα refer to in θα τα επιστρέψω and why is it τα?

Τα is a neuter plural object pronoun meaning them.

It refers to some previously mentioned neuter plural noun, such as:

τα παπούτσια (the shoes)
τα ρούχα (the clothes)
τα προϊόντα (the products)

Since these nouns are neuter plural, the correct pronoun is also neuter plural:

Θα τα επιστρέψω. = I will return them.

If the thing were feminine plural, you’d use τις; for masculine plural, τους, e.g.:

Θα τις επιστρέψω. (feminine plural)
Θα τους επιστρέψω. (masculine plural)

Why is the pronoun τα placed before the verb (θα τα επιστρέψω) and not after, like in English?

Greek object pronouns are clitics: they normally go before a finite verb when used with θα, δεν, etc.

Correct word order with θα:

θα τα επιστρέψω (I will return them)
θα το δω (I will see it)
θα σου πω (I will tell you)

You cannot place the pronoun after the verb like in English:

θα επιστρέψω τα ❌ (wrong)
It must be θα τα επιστρέψω ✅

So the structure is:
θα + pronoun + verb

Why can the subject εγώ be left out? How do we know it means “I will return them”?

Greek is a pro-drop language: it usually omits subject pronouns because the verb ending already shows the subject.

επιστρέφω = I return
επιστρέφεις = you (sg.) return
επιστρέφει = he/she/it returns

So θα επιστρέψω clearly means I will return without needing εγώ.

You could say Εγώ θα τα επιστρέψω to emphasize I (e.g. “I will return them, not someone else”), but the neutral, normal sentence drops εγώ:

Αν το μέγεθος δεν είναι σωστό, θα τα επιστρέψω…

What’s the difference between επιστρέφω and a verb like γυρίζω πίσω for “return”?

Both can involve the idea of “return,” but they’re used differently:

επιστρέφω κάτι = to return something (more formal/literal, common with goods, money, books)
- Θα τα επιστρέψω. = I will return them (to the shop).
γυρίζω πίσω = to come/go back (often intransitive, about you returning, not an object)
- Θα γυρίσω πίσω αύριο. = I will come back tomorrow.

For returning items to a store, επιστρέφω is the natural verb:

Θα τα επιστρέψω στο κατάστημα. = I will return them to the store.

What does θα do in θα τα επιστρέψω and θα τα ανταλλάξω?

Θα is the particle that marks the future tense in modern Greek.

επιστρέφω = I return
θα επιστρέψω = I will return
ανταλλάζω = I exchange
θα ανταλλάξω = I will exchange

In this sentence:

θα τα επιστρέψω = I will return them
(και) θα τα ανταλλάξω = and I will exchange them

The verb form (e.g. επιστρέψω, ανταλλάξω) here is the perfective (aorist) stem, but together with θα it simply makes a normal future with a sense of a single, complete action in the future.

What does ανταλλάξω mean, and how is ανταλλάξω με κάτι άλλο structured?

Ανταλλάζω means to exchange / to swap.

With θα, we get the future:

θα ανταλλάξω = I will exchange

The structure is:

ανταλλάζω κάτι με κάτι = I exchange something with/for something (else)

So:

θα τα ανταλλάξω με κάτι άλλο
= I will exchange them for something else.
τα = them (the items)
με = with/for
κάτι άλλο = something else

You keep the same pattern for other nouns:

Θα ανταλλάξω το πουκάμισο με ένα μεγαλύτερο.
I’ll exchange the shirt for a bigger one.

Why is it με κάτι άλλο and not σε κάτι άλλο or για κάτι άλλο?

The verb ανταλλάζω naturally takes με when you say exchange A for/with B:

ανταλλάζω Α με Β

Examples:

Θα ανταλλάξω αυτό το βιβλίο με ένα άλλο.
I’ll exchange this book for another one.
Θα τα ανταλλάξω με κάτι άλλο.
I’ll exchange them for something else.

Σε or για would sound wrong or at least unnatural here. It’s mainly a matter of verb + preposition usage: ανταλλάζω goes with με in this meaning.

What does κάτι άλλο literally mean, and why are both words neuter?

Κάτι άλλο literally means “something other” = something else.

κάτι = something (indefinite neuter)
άλλο = other/different (neuter singular, agreeing with an understood thing)

In Greek, κάτι is grammatically neuter singular, so any adjective describing it is also neuter singular:

κάτι καλό = something good
κάτι περίεργο = something strange
κάτι άλλο = something else

That’s why άλλο appears in the neuter form here.

Why is there a comma after σωστό: Αν το μέγεθος δεν είναι σωστό, θα τα επιστρέψω…?

In Greek, it’s standard to use a comma between the if-clause and the main clause, just like in English when the if-clause comes first.

Αν το μέγεθος δεν είναι σωστό, θα τα επιστρέψω…
Όταν τελειώσω, θα φύγω.

If the order is reversed, the comma is often omitted:

Θα τα επιστρέψω, αν το μέγεθος δεν είναι σωστό. (comma often optional)
Θα φύγω όταν τελειώσω. (no comma)

So the comma here is normal punctuation marking the break between condition and result.