Learn Hardcore Greek: Μέχρι να τελειώσει η μέρα της, η νοσοκόμα θα έχει βοηθήσει πολλούς ανθρώπους. - By the time her day ends, the nurse will have helped many people.

In modern Greek, when μέχρι (‘until / by the time’) is followed by a clause (a whole sentence with a verb), it normally takes να + subjunctive:

μέχρι να + subjunctive
→ μέχρι να τελειώσει η μέρα της
“until / by the time her day ends”

You cannot drop να here; ✗ μέχρι τελειώσει is wrong in standard modern Greek.

Why not τελειώνει?
Because temporal clauses referring to the future use the subjunctive, not the present indicative:

μέχρι να τελειώσει η μέρα της
Literally: “until her day finish (subj.)” → “by the time her day is over”

Using τελειώνει would sound like you’re talking about something habitual or ongoing, not a specific future endpoint.

Is τελειώσει a past tense? Why does a “past-looking” form talk about the future?

Formally, τελειώσει is the perfective subjunctive (often built on the same stem as the aorist), 3rd person singular of τελειώσω.

Greek uses two aspects in the subjunctive:

Perfective subjunctive: να τελειώσει – focuses on the event as a whole / completed.
Imperfective subjunctive: να τελειώνει – focuses on ongoing / repeated action.

In μέχρι να τελειώσει η μέρα της, the focus is on the completion of her day, not the process of it passing, so Greek uses the perfective form.

It looks like a “past” stem to an English speaker because it’s related to the aorist, but in Greek it isn’t inherently past here; it’s aspect + mood, and the “future” sense comes from the whole structure μέχρι να + subjunctive.

Why does the main verb use θα έχει βοηθήσει instead of the simpler θα βοηθήσει?

θα βοηθήσει = simple future, “she will help”
θα έχει βοηθήσει = future perfect, “she will have helped”

The future perfect describes an action that will be completed before a certain future point:

Reference point: μέχρι να τελειώσει η μέρα της (“by the time her day is over”).
Action: θα έχει βοηθήσει πολλούς ανθρώπους (“she will have helped many people,” i.e. that helping will already be finished by then).

So the structure is:

By the time X happens, Y will already be completed.

Greek expresses this with θα + έχω + perfective form:

θα έχει βοηθήσει
= will have helped

How is the future perfect θα έχει βοηθήσει formed in Greek?

Future perfect is a compound tense:

θα (future particle) +
a present-tense form of έχω (“to have”) +
the perfective non-past form of the main verb (the form you also use with έχω in the present perfect).

For βοηθάω / βοηθώ (to help):

Present perfect:
- έχει βοηθήσει = “(he/she) has helped”
Future perfect:
- θα έχει βοηθήσει = “(he/she) will have helped”

Other examples:

έχω γράψει → “I have written”
θα έχω γράψει → “I will have written”
έχει τελειώσει → “it has finished”
θα έχει τελειώσει → “it will have finished”

Why is it η μέρα της and not τη μέρα της?

Case matters here:

η μέρα της is nominative (subject of the verb).
τη μέρα της is accusative (direct object).

In this clause, the day is the subject of τελειώσει:

η μέρα της (subject) να τελειώσει (verb)
Literally: “until her day finishes”

If you wrote τη μέρα της, you’d be treating “her day” as an object, which doesn’t fit the meaning here.

So η μέρα must be in the nominative: η μέρα της.

What exactly is της doing in η μέρα της? Why does it come after the noun?

της here is a clitic possessive pronoun in the genitive (“her”).

In modern Greek, possessive pronouns usually come after the noun:

η μέρα της = “her day”
το βιβλίο του = “his book”
το σπίτι τους = “their house”

The pattern is:

article + noun + (clitic) possessive

You don’t normally put it before the noun, so forms like ✗ η της μέρα are ungrammatical in standard modern Greek.

You could also say:

η μέρα της νοσοκόμας = “the day of the nurse”
(more explicit; “of the nurse” rather than just “her”)

Why is it η νοσοκόμα with an article? In English we can just say “a nurse”.

Greek uses the definite article much more than English, especially:

With professions or roles used in a generic sense:
- Η νοσοκόμα δουλεύει πολύ.
  “The nurse works a lot.” = “Nurses work a lot / The nurse (in question) works a lot.”

In this sentence, η νοσοκόμα can mean:

“the nurse” (a specific one whose day we’re talking about), or
more generally “a nurse” / “a nurse of that type” in the context.

Leaving out the article (✗ νοσοκόμα θα έχει βοηθήσει…) is possible but much more limited and usually sounds incomplete here. The safe default with singular, specific persons is:

article + noun → η νοσοκόμα

Why is it πολλούς ανθρώπους and not πολύ ανθρώπους?

πολλούς is the correct inflected form of “many” here.

πολύς, πολλή, πολύ is the base adjective “a lot, much/many”.
It agrees in gender, number, and case with the noun.

άνθρωπος (person/human) is:

masculine,
plural here,
and in the accusative (direct object of “helped”).

So we need the masculine plural accusative of πολύς:

masculine plural nominative: πολλοί άνθρωποι
masculine plural accusative: πολλούς ανθρώπους

Hence:

πολλούς ανθρώπους = “many people” (as the object of the verb).

πολύ ανθρώπους is incorrect in standard grammar for this role.

Why is ανθρώπους (accusative plural) used instead of άνθρωποι?

Because άνθρωποι (nominative plural) is used for the subject, while ανθρώπους (accusative plural) is used for the direct object.

Here, πολλούς ανθρώπους is what the nurse has helped → it’s the object of θα έχει βοηθήσει:

Subject: η νοσοκόμα
Verb: θα έχει βοηθήσει
Direct object: πολλούς ανθρώπους

So we must use the accusative plural: ανθρώπους, not άνθρωποι.

What’s the difference in meaning between θα έχει βοηθήσει πολλούς ανθρώπους and θα βοηθήσει πολλούς ανθρώπους?

Both are future, but they have different time perspectives:

θα βοηθήσει πολλούς ανθρώπους
→ “She will help many people.”
Neutral future: at some point in the future, she will help many people.
θα έχει βοηθήσει πολλούς ανθρώπους
→ “She will have helped many people.”
Focus on completion by a future deadline. At that future point (when her day is over), that helping is already done.

In your full sentence, because you have μέχρι να τελειώσει η μέρα της, the future perfect fits especially well:

By the time her day ends, this helping will already be completed.

Could the time clause go at the end, like in English: “The nurse will have helped many people by the time her day is over”?

Yes. Greek word order is quite flexible. You can say:

Η νοσοκόμα θα έχει βοηθήσει πολλούς ανθρώπους, μέχρι να τελειώσει η μέρα της.

This is fully natural and means the same thing.

The two main options:

Μέχρι να τελειώσει η μέρα της, η νοσοκόμα θα έχει βοηθήσει πολλούς ανθρώπους.
Η νοσοκόμα θα έχει βοηθήσει πολλούς ανθρώπους, μέχρι να τελειώσει η μέρα της.

Only punctuation and emphasis change slightly; the core meaning is identical.

Is there any difference between μέχρι να τελειώσει η μέρα της and a phrase like ως το τέλος της μέρας της?

They are very close in meaning, but not identical in structure:

μέχρι να τελειώσει η μέρα της
“until (the moment when) her day ends”
→ a clause with a verb (τελειώσει) in the subjunctive.
ως το τέλος της μέρας της
“until the end of her day / by the end of her day”
→ a prepositional phrase with a noun (το τέλος).

You could rewrite the sentence as:

Ως το τέλος της μέρας της, η νοσοκόμα θα έχει βοηθήσει πολλούς ανθρώπους.

This is also correct and very natural. The difference is stylistic more than grammatical; μέχρι να + verb highlights the event (“her day ends”), while ως το τέλος highlights the time point (“the end”).