Learn Hardcore Greek: Η διάλεξη διαρκεί δύο ώρες και στο τέλος ο καθηγητής δηλώνει ότι η παρουσία μας είναι απαραίτητη. - The lecture lasts two hours and at the end the professor states that our presence is necessary.

κρατάει is more colloquial and very common in everyday speech
- Η διάλεξη κρατάει δύο ώρες.
διαρκεί is a bit more neutral/formal and is very natural in written language, academic contexts, news, etc.

Both are correct. If you are speaking informally with friends, κρατάει is slightly more expected; in writing or more formal speech, διαρκεί fits very well.

Why is δύο ώρες in the accusative case, and why don’t we need a preposition like “for” (as in “for two hours”)?

In Greek, duration of time is usually expressed in the accusative case without a preposition.

δύο ώρες is the accusative plural of η ώρα (hour).
So διαρκεί δύο ώρες literally means “it lasts two hours”, and the accusative here answers “for how long?”.

Other examples:

Περίμενα μία ώρα. – I waited (for) one hour.
Θα λείψω τρεις μέρες. – I’ll be away (for) three days.

You can sometimes add για:

διαρκεί για δύο ώρες

…but in this type of sentence it’s often omitted, and διαρκεί δύο ώρες is the most natural.

What exactly is στο τέλος and why do we need the article το?

στο τέλος is the contraction of σε + το τέλος:

σε = in, at, to (a very general preposition)
το τέλος = the end (neuter noun)

So στο τέλος literally means “at the end”.

Why the article το?
In Greek, abstract nouns like το τέλος very often take the definite article even when English would not use “the”:

στο τέλος – at the end
στην αρχή – at the beginning
στη μέση – in the middle

So και στο τέλος ο καθηγητής… = “and at the end the professor…”.

Why is it ο καθηγητής with the article? Could I just say καθηγητής δηλώνει?

In Greek, definite articles are used much more frequently than in English.

ο καθηγητής = “the professor / the lecturer”

When you are talking about a specific person that both speaker and listener know (e.g. the professor of this course), Greek will almost always use the article:

Ο καθηγητής μπήκε στην αίθουσα. – The professor entered the room.

Leaving out the article (καθηγητής δηλώνει) is usually either:

ungrammatical in this context, or
would sound like you’re speaking in headlines or very telegraphic style.

So in this sentence, ο καθηγητής with the article is required.

What does δηλώνει mean here, and how is it different from λέει or ανακοινώνει?

Δηλώνει comes from δηλώνω, which means “to state, to declare, to make a formal statement.”

Nuance:

λέω = to say, tell
- neutral, basic verb: ο καθηγητής λέει ότι…
δηλώνω = to state/declare in a more official or explicit way
- ο καθηγητής δηλώνει ότι… suggests something like “he formally states/declares that…”
ανακοινώνω = to announce
- implies addressing a group with new information: ο καθηγητής ανακοινώνει ότι…

In this sentence, δηλώνει makes it sound like the professor is explicitly and perhaps somewhat formally stating that the presence is necessary, not just casually mentioning it.

What is the role of ότι after δηλώνει? Is it the same as “that” in English, and how is it different from πως?

Yes, ότι here functions just like English “that” introducing a content clause:

ο καθηγητής δηλώνει ότι η παρουσία μας είναι απαραίτητη
= “the professor states that our presence is necessary.”

ότι vs πως:

In modern Greek, in this usage, ότι and πως often mean the same thing:
- δηλώνει ότι… / δηλώνει πως…
ότι is a bit more neutral/standard; πως may feel slightly more colloquial in some contexts.

Be careful not to confuse ότι (conjunction “that”) with ό,τι (with a comma), which means “whatever / anything that.” In your sentence, it’s the conjunction, so ότι without comma.

What does η παρουσία μας literally mean, and why does μας come after the noun?

η παρουσία μας literally means “our presence”:

η παρουσία = presence (feminine noun)
μας = our (also “us” as object; same form)

In Greek, the common way to say “our X” is:

το/η/ο + noun + μας

So:

η παρουσία μας – our presence
ο καθηγητής μας – our professor
το βιβλίο μας – our book

The possessive pronoun μας is enclitic here: it usually follows the noun, not precedes it like “our” in English.

You could also say η δική μας παρουσία (“our own presence”) for emphasis, but the normal structure is η παρουσία μας.

Why is απαραίτητη feminine, and how does it agree with η παρουσία?

In Greek, adjectives agree with the noun they modify in gender, number, and case.

η παρουσία is:
- feminine
- singular
- nominative (subject of the verb είναι)
Therefore, the adjective απαραίτητος (“necessary”) must also be:
- feminine
- singular
- nominative: απαραίτητη.

So we get:

η παρουσία μας είναι απαραίτητη.
- η (fem. sg. nom.)
- παρουσία (fem. sg. nom.)
- απαραίτητη (fem. sg. nom.)

If the subject were masculine or neuter, the form would change:

Ο καθηγητής είναι απαραίτητος. – The professor is necessary.
Το βιβλίο είναι απαραίτητο. – The book is necessary.

Could we say η παρουσία μας είναι υποχρεωτική instead of απαραίτητη? Is there a difference?

Both are possible, but they differ slightly in nuance:

απαραίτητη = necessary, essential, indispensable
- Suggests that without our presence, something important is missing.
υποχρεωτική = compulsory, mandatory
- Stronger sense of obligation (like a rule or requirement).

So:

η παρουσία μας είναι απαραίτητη
= Our presence is necessary (maybe strongly recommended / essential).
η παρουσία μας είναι υποχρεωτική
= Our presence is compulsory (you must attend; it’s a rule).

In many academic contexts, you might actually hear υποχρεωτική if attendance is formally required.

Is the word order Η διάλεξη διαρκεί δύο ώρες fixed, or could I say Διαρκεί δύο ώρες η διάλεξη?

Greek word order is more flexible than English.

Both of these are grammatically correct:

Η διάλεξη διαρκεί δύο ώρες.
Διαρκεί δύο ώρες η διάλεξη.

Difference:

(1) is the most neutral / standard. Subject (η διάλεξη) first, then verb.
(2) puts slight emphasis on the duration or on the verb, and the subject appears later. It can sound a bit more stylistic or emphatic, depending on context.

In everyday speech and writing, the original order (Η διάλεξη διαρκεί δύο ώρες) is what you should use by default.

Why is the present tense (διαρκεί, δηλώνει, είναι) used? In English we might also say “the lecture will last two hours.”

Greek often uses the present tense:

To describe general truths or typical facts:
- Η γη γυρίζει γύρω από τον ήλιο. – The earth revolves around the sun.
To talk about scheduled future events (similar to English present simple):
- Αύριο το μάθημα αρχίζει στις 9. – Tomorrow the class starts at 9.

In your sentence, present can be:

a general description of how the lecture is structured, or
a description of a regular event (every week, the lecture lasts two hours and at the end the professor says this).

We could also talk about a specific future lecture in present tense in Greek:

Αύριο η διάλεξη διαρκεί δύο ώρες. – Tomorrow the lecture lasts / will last two hours.

So the Greek present tense covers both present and certain future meanings, very much like English “The lecture starts at nine tomorrow.”

What exactly is the form of διαρκεί, δηλώνει, and είναι grammatically?

All three are 3rd person singular, present indicative, active (except είναι, which is from the irregular verb “to be”).

διαρκεί
- from διαρκώ (to last)
- 3rd pers. sg. present: “he/she/it lasts”
δηλώνει
- from δηλώνω (to state/declare)
- 3rd pers. sg. present: “he/she/it states”
είναι
- from είμαι (to be)
- 3rd pers. sg. present: “he/she/it is”

Each one agrees with a third-person singular subject:

η διάλεξη διαρκεί… (lecture – it lasts)
ο καθηγητής δηλώνει… (professor – he states)
η παρουσία μας είναι… (presence – it is)

Can you break down the whole sentence word by word with basic glosses?

Sure, very literally:

Η – the (fem. sg. nom.)
διάλεξη – lecture
διαρκεί – lasts
δύο – two
ώρες – hours (fem. pl. acc.)
και – and
στο – in/at the (σε + το)
τέλος – end (neut. sg.)
ο – the (masc. sg. nom.)
καθηγητής – professor / lecturer
δηλώνει – states / declares
ότι – that (conjunction)
η – the (fem. sg. nom.)
παρουσία – presence
μας – our
είναι – is
απαραίτητη – necessary, essential (fem. sg. nom.)