Μιλάει με βεβαιότητα, γιατί έχει ήδη ελέγξει όλες τις λεπτομέρειες.

Greek often leaves subject pronouns unstated when they are clear from the verb form. Here, Μιλάει and έχει are both third person singular, so the subject is understood as he, she, or sometimes it, depending on context.

So Greek does not need to say Αυτός/Αυτή unless the speaker wants extra emphasis or contrast.

Μιλάει is the present tense of μιλάω / μιλώ and means he/she speaks or he/she is speaking.

Like the Greek present tense in general, it can describe:

• a general/habitual action: He/She speaks with certainty
• an action happening now: He/She is speaking with certainty

The exact English translation depends on context.

Both are correct.

They are two common present-tense forms of the same verb:

• μιλάει
• μιλά

In everyday Modern Greek, μιλάει is very common and natural. μιλά is also standard, just shorter. A learner will see and hear both.

Greek very often uses με + noun to express manner.

So:

• με βεβαιότητα = with certainty
• natural English translation: confidently, with confidence, or with certainty, depending on context

This phrase is perfectly normal Greek. It is more literally with certainty than a one-word English adverb.

Also, βεβαιότητα suggests certainty or assurance, not just general self-confidence.

Here γιατί means because.

This is important because γιατί can also mean why in a question:

• Γιατί μιλάει έτσι; = Why is he/she speaking like that?
• Μιλάει έτσι, γιατί ξέρει το θέμα. = He/She speaks like that because he/she knows the subject.

So the same word can mean either why or because; the sentence structure tells you which meaning is intended.

The comma separates the main clause from the reason clause.

• Μιλάει με βεβαιότητα = main clause
• γιατί έχει ήδη ελέγξει όλες τις λεπτομέρειες = subordinate clause explaining the reason

In Greek, a comma before a γιατί clause meaning because is very common and standard.

It is the present perfect.

It is formed with:

• έχει = has
• ελέγξει = the form used to complete the perfect construction

So:

• έχει ήδη ελέγξει = has already checked

This shows that the checking is completed before now, and that result matters in the present. That is why the person can speak with certainty now.

After έχω in the perfect tense, Greek uses a special non-finite verb form:

• έχω γράψει
• έχω δει
• έχω ελέγξει

So ελέγξει here does not mean he/she checks by itself. It is the form that combines with έχει to mean has checked.

You may notice it looks like the form used after να:

• να ελέγξει
• έχει ελέγξει

That similarity is normal.

Ήδη means already.

In this sentence it appears in a very natural position:

• έχει ήδη ελέγξει

That is a common place for it: between the auxiliary verb and the main verb form.

You can sometimes move ήδη for emphasis, for example:

• Ήδη έχει ελέγξει όλες τις λεπτομέρειες but the original order is very neutral and natural.

Because λεπτομέρειες is a feminine plural noun, and the words that go with it must match it.

• όλες = all (feminine plural)
• τις = the (feminine plural accusative)
• λεπτομέρειες = details

So όλες τις λεπτομέρειες means all the details.

Greek usually keeps the article in this kind of phrase, so όλες τις λεπτομέρειες is the normal structure, not just όλες λεπτομέρειες.

It is accusative plural, because it is the direct object of ελέγξει.

The person has checked what?

• όλες τις λεπτομέρειες

That makes it the object, so Greek uses the accusative.

A useful comparison:

• nominative plural: οι λεπτομέρειες = the details (subject)
• accusative plural: τις λεπτομέρειες = the details (object)

English does not show this difference clearly, but Greek does.

Greek word order is fairly flexible, but the original sentence is a very natural, neutral way to say it.

Original:

• Μιλάει με βεβαιότητα, γιατί έχει ήδη ελέγξει όλες τις λεπτομέρειες.

You could rearrange it for emphasis, for example:

• Γιατί έχει ήδη ελέγξει όλες τις λεπτομέρειες, μιλάει με βεβαιότητα.

But that sounds more marked and less neutral. For ordinary use, the original order is better.

Yes. In Greek, the accent marks show which syllable gets the stress.

For example:

• Μιλάει → stress on λά
• βεβαιότητα → stress on ό
• γιατί → stress on τί
• έχει → stress on έ
• ελέγξει → stress on λέγ
• όλες → stress on ό
• λεπτομέρειες → stress on μέ

Stress is important in Greek pronunciation, so learners should pay close attention to the written accents.