Δεν μπορώ να ξεχωρίσω αυτή τη λέξη από την άλλη όταν μιλάς τόσο γρήγορα.

In Modern Greek, μπορώ is normally followed by να + a verb:

• μπορώ να πάω = I can go
• μπορώ να δω = I can see
• μπορώ να ξεχωρίσω = I can distinguish

So δεν μπορώ να ξεχωρίσω literally means I am not able to distinguish.

This is a very common structure:

• μπορώ να... = can / be able to...
• δεν μπορώ να... = cannot / am not able to...

This is a very common learner question, because Greek often uses different verb forms after να.

• ξεχωρίζω = present/imperfective stem
• ξεχωρίσω = aorist/perfective stem

After να, Greek can use either a present-type form or an aorist-type form, depending on how the action is viewed.

Here, να ξεχωρίσω presents the action as a complete event: to manage to tell one word apart from the other. That is why it sounds natural here.

Compare:

• Δεν μπορώ να ξεχωρίσω αυτή τη λέξη από την άλλη.
  = I can’t tell this word apart from the other one.

• Δεν μπορώ να ξεχωρίζω...
  would sound less natural here, and would suggest more of an ongoing/habitual process.

So in this sentence, ξεχωρίσω is the normal choice.

Here it means to distinguish, to tell apart, or to differentiate.

So:

• ξεχωρίζω αυτή τη λέξη από την άλλη
  = I distinguish this word from the other one
  = I tell this word apart from the other one

A very useful pattern is:

• ξεχωρίζω Α από Β
  = I distinguish A from B

In other contexts, ξεχωρίζω can also mean:

• to stand out
• to separate
• to single out

But in this sentence, the meaning is clearly distinguish / tell apart.

Greek usually uses the article together with this/that.

So:

• αυτή η λέξη = this word
• αυτή τη λέξη = this word (in the accusative case)

Greek normally says:

• αυτή η γυναίκα = this woman
• αυτό το βιβλίο = this book
• αυτή τη λέξη = this word

Using αυτή λέξη without the article would sound wrong in standard Greek.

The full accusative feminine singular article is την, but the final -ν is often dropped before certain consonants in everyday spelling and speech.

So both of these may appear:

• την άλλη
• τη λέξη

The difference depends on the sound that follows.

Before some consonants, Greek often drops the final -ν:

• τη λέξη
• τη μέρα

But before vowels and certain consonants, it is usually kept:

• την άλλη
• την πόρτα
• την καρδιά

So in your sentence:

• αυτή τη λέξη
• από την άλλη

That is completely normal.

Good observation: in Greek, some feminine nouns do change visibly in the accusative, but some do not change much.

λέξη is feminine singular, and its nominative and accusative singular are the same in form:

• nominative: η λέξη = the word
• accusative: τη λέξη = the word

So even though it is the direct object after ξεχωρίσω, the noun itself stays λέξη. The article shows the case more clearly than the noun does.

Greek often leaves out a noun if it is already understood from context.

So:

• από την άλλη
  literally = from the other [one]

Here, λέξη is understood:

• από την άλλη (λέξη)
  = from the other word

This is very natural in Greek and in English too:

• this word from the other
• more natural English: this word from the other one

So άλλη is functioning like the other one.

With ξεχωρίζω, Greek commonly uses από to mark what something is being distinguished from.

Pattern:

• ξεχωρίζω κάτι από κάτι άλλο
• distinguish something from something else

So:

• ξεχωρίσω αυτή τη λέξη από την άλλη = distinguish this word from the other one

This is one of those combinations worth memorizing:

• ξεχωρίζω ... από ...

In Modern Greek, από takes the accusative.

That is why you get:

• από την άλλη
• από τον φίλο
• από το σπίτι

So in this sentence, την άλλη is accusative because it follows από.

Μιλάς is 2nd person singular of μιλάω / μιλώ:

• μιλάω / μιλώ = I speak
• μιλάς = you speak

So:

• όταν μιλάς τόσο γρήγορα = when you speak so quickly

This is informal singular you. If you were speaking formally or to more than one person, you would use:

• όταν μιλάτε τόσο γρήγορα

Greek usually leaves out subject pronouns when they are not needed, because the verb ending already shows the person.

Here:

• μιλάς already means you speak

So Greek does not need to say εσύ unless it wants emphasis or contrast.

Compare:

• όταν μιλάς τόσο γρήγορα = when you speak so quickly
• όταν εσύ μιλάς τόσο γρήγορα = when you speak so quickly

The second version is more emphatic.

τόσο means so, so much, or that depending on context.

γρήγορα means quickly / fast.

Together:

• τόσο γρήγορα = so quickly / so fast

Examples:

• Μιλάς τόσο γρήγορα. = You speak so quickly.
• Τρέχει τόσο γρήγορα. = He/she runs so fast.

So in this sentence, it explains the reason the speaker cannot distinguish the words.

Because it is modifying the verb μιλάς.

• adjectives describe nouns
• adverbs describe verbs

Here we need an adverb:

• μιλάς γρήγορα = you speak quickly

Compare:

• γρήγορος άνθρωπος = a quick/fast person
• μιλάει γρήγορα = he/she speaks quickly

So γρήγορα is the correct adverb form.

όταν means when.

It introduces a time clause:

• όταν μιλάς τόσο γρήγορα = when you speak so quickly

So the structure is:

• Δεν μπορώ να ξεχωρίσω αυτή τη λέξη από την άλλη
  main clause
• όταν μιλάς τόσο γρήγορα
  time clause

You can think of it as: I can’t distinguish this word from the other one when you speak so quickly.

Yes. Greek word order is fairly flexible, although some orders sound more natural than others depending on emphasis.

The original sentence:

• Δεν μπορώ να ξεχωρίσω αυτή τη λέξη από την άλλη όταν μιλάς τόσο γρήγορα.

You could also say:

• Όταν μιλάς τόσο γρήγορα, δεν μπορώ να ξεχωρίσω αυτή τη λέξη από την άλλη.

That version puts the when clause first and may sound a little more natural in some contexts.

Greek often changes word order for emphasis, rhythm, or style, while the endings and articles help keep the meaning clear.

Because it has the article την and because the noun is understood from context.

• άλλη by itself = other / another
• η άλλη / την άλλη = the other one

In this sentence, the speaker is comparing two words:

• αυτή τη λέξη = this word
• την άλλη = the other one

So την άλλη naturally means the other word or the other one.

Yes.

• μπορώ = I can
• δεν μπορώ = I can’t

δεν is the normal negation used with finite verbs in Modern Greek.

So:

• Μπορώ να ξεχωρίσω... = I can distinguish...
• Δεν μπορώ να ξεχωρίσω... = I can’t distinguish...

αυτή is pronounced roughly like af-TI or av-TI, depending on the following sound and natural speech patterns, but for learners the key point is the stress on the last syllable: -τή.

You may also see αυτήν in some contexts. The extra -ν is similar to what happens with articles like τη / την. In everyday Modern Greek, the final -ν may appear or disappear depending on style, pronunciation, and what follows.

So in your sentence, αυτή τη λέξη is a perfectly normal form.

Yes. You could say:

• Δεν μπορώ να ξεχωρίσω αυτή τη λέξη από την άλλη λέξη όταν μιλάς τόσο γρήγορα.

But this sounds more repetitive. Greek, like English, often leaves out repeated nouns when they are obvious.

So από την άλλη is more natural than repeating λέξη.

A useful breakdown is:

• Δεν μπορώ = I can’t
• να ξεχωρίσω = distinguish / tell apart
• αυτή τη λέξη = this word
• από την άλλη = from the other one
• όταν μιλάς τόσο γρήγορα = when you speak so quickly

So the structure is:

[negation + can] + [να + verb] + [object] + [από + comparison] + [when-clause]

This is a very natural Greek sentence pattern, and you can reuse it with other vocabulary. For example:

• Δεν μπορώ να ξεχωρίσω τη μία φωνή από την άλλη.
  = I can’t distinguish one voice from the other.

• Δεν μπορώ να ξεχωρίσω αυτό το όνομα από το άλλο.
  = I can’t tell this name apart from the other one.