Learn Hardcore Greek: Η διάρκεια του μαθήματος σήμερα ήταν μία ώρα, αλλά ένιωσα ότι πέρασε πολύ γρήγορα. - The duration of the lesson today was one hour, but I felt that it passed very quickly.

The phrase η διάρκεια του μαθήματος literally means the duration of the lesson.
Greek often uses the genitive to show possession or a relationship, just like of in English.

So the structure is:

Η διάρκεια (the duration)
του μαθήματος (of the lesson)

Together: Η διάρκεια του μαθήματος = The duration of the lesson.

Could σήμερα go in another place in the sentence, or must it be after του μαθήματος?

σήμερα (today) is fairly flexible in word order. All of these are possible and natural, with small differences in emphasis:

Η διάρκεια του μαθήματος σήμερα ήταν μία ώρα… (as in the original)
Η διάρκεια του σημερινού μαθήματος ήταν μία ώρα… (more like: the duration of today’s lesson…)
Σήμερα η διάρκεια του μαθήματος ήταν μία ώρα… (emphasis on today as a whole)
Η διάρκεια του μαθήματος ήταν σήμερα μία ώρα… (less common, but possible)

Greek word order is more flexible than English; adverbs of time like σήμερα can move around, as long as the meaning stays clear and the sentence sounds natural.

What does μία ώρα mean exactly, and how is μία different from μια?

μία ώρα means one hour.

ώρα is a feminine noun: η ώρα = the hour.
μία is the feminine form of the numeral one (masculine: ένας, neuter: ένα).

About μία vs μια:

μία and μια are usually pronounced the same (mia).
μία is a bit more formal or used when you want to stress the number one.
μια is more common in everyday writing and speech, especially when it acts like an indefinite article (a/an).

In this sentence, both μία ώρα and μια ώρα are acceptable in practice, though μία is slightly more explicit as the numeral one.

Why is the verb ήταν used here and not είναι?

ήταν is the past tense (imperfect) of είμαι (to be).

είναι = is / are (present)
ήταν = was / were (past)

The sentence refers to a lesson that already happened today, so Greek uses the past form:

Η διάρκεια του μαθήματος σήμερα ήταν μία ώρα…
= The duration of the lesson today was one hour…

Using είναι would put it in the present, which would not match the meaning (unless you are somehow talking about an ongoing lesson, which you are not here).

What is ένιωσα from, and what tense is it?

ένιωσα is the aorist (simple past) of the verb νιώθω (to feel).

Present: νιώθω = I feel
Aorist (simple past): ένιωσα = I felt (completed action)

So αλλά ένιωσα ότι… means but I felt that… referring to one completed feeling at that moment, not a continuous feeling over time.

What is the difference between ένιωσα and ένιωθα?

Both come from νιώθω (to feel), but they express different aspects of the past:

ένιωσα = aorist (simple past)
- Focus on a single, completed event: I felt (at that moment).
- In this sentence, it is like: I got the impression that it passed very quickly.
ένιωθα = imperfect (continuous past)
- Focus on an ongoing or repeated feeling in the past: I was feeling / I used to feel.

If you said:

…αλλά ένιωθα ότι περνούσε πολύ γρήγορα.

you would be emphasizing a more continuous or repeated feeling (I was feeling that it was passing very quickly), which is a bit heavier and less natural for this simple comment about a finished lesson.

How is ότι used here, and what is the difference between ότι, πως, and ό,τι?

In the sentence, ότι introduces a that-clause, just like that in English:

ένιωσα ότι πέρασε πολύ γρήγορα
= I felt that it passed very quickly.

Differences:

ότι (without comma, one word)
- Conjunction meaning that (introduces a clause).
- Example: Ξέρω ότι έχεις δίκιο. = I know that you are right.
πως (when used as a conjunction)
- Often interchangeable with ότι in modern Greek, also meaning that.
- In this sentence, you could also say:
  …αλλά ένιωσα πως πέρασε πολύ γρήγορα.
ό,τι (with a comma)
- Pronoun meaning whatever / anything that.
- Example: Φάε ό,τι θέλεις. = Eat whatever you want.

So here you need ότι (or πως), not ό,τι.

What does πέρασε literally mean, and how does it work with time?

πέρασε is the aorist (simple past) of περνάω / περνώ, which literally means to pass.

Present: περνάω = I pass / I spend (time)
Aorist: πέρασα = I passed / I spent

In the 3rd person singular:

πέρασε = it passed

When talking about time, περνάω is used the same way as English time passes:

Πέρασε η ώρα. = The hour passed.
Πέρασε πολύ γρήγορα. = It passed very quickly.

So in the sentence, πέρασε πολύ γρήγορα means (it) passed very quickly, where it is the time of the lesson.

What is the subject of πέρασε? Why is it not shown?

The grammatical subject is not written explicitly, but it is understood from context.

It can be interpreted as:

η ώρα (the hour)
or το μάθημα (the lesson)
or more generally ο χρόνος (the time)

Greek often omits pronouns or even nouns when they are clear from context. Here, after η διάρκεια του μαθήματος σήμερα ήταν μία ώρα, the listener naturally understands that the time of the lesson is what passed quickly. So Greek simply says:

…αλλά ένιωσα ότι πέρασε πολύ γρήγορα.
= …but I felt that it passed very quickly.

No explicit αυτό or η ώρα is necessary.

Why is it πολύ γρήγορα and not πολύ γρήγορο or πολύ γρήγορη?

Because here we need an adverb, not an adjective.

γρήγορος (m.), γρήγορη (f.), γρήγορο (n.) are adjectives: fast / quick (describing nouns).
γρήγορα is the adverb: quickly / fast (describing verbs).

In the sentence:

πέρασε = it passed (verb)
πολύ γρήγορα = very quickly (adverb phrase modifying the verb πέρασε)

So:

πέρασε πολύ γρήγορα = it passed very quickly.

If you said πολύ γρήγορο or πολύ γρήγορη, you would be describing a thing (a noun), not the way it passed.

Does πολύ modify πέρασε or γρήγορα, and can its position change?

In πέρασε πολύ γρήγορα, πολύ primarily modifies γρήγορα:

γρήγορα = quickly
πολύ γρήγορα = very quickly

So the verb phrase is:

πέρασε [πολύ γρήγορα] = it passed [very quickly]

You would normally keep πολύ immediately before γρήγορα.
Other positions like πέρασε γρήγορα πολύ sound unnatural in modern Greek in this context.

Could you express the same idea without using διάρκεια? For example, using a simpler verb for a beginner?

Yes, you can say the same idea in a more straightforward way. For example:

Το μάθημα σήμερα κράτησε μία ώρα, αλλά ένιωσα ότι τελείωσε πολύ γρήγορα.

Breakdown:

Το μάθημα σήμερα = The lesson today
κράτησε μία ώρα = lasted one hour
αλλά ένιωσα ότι = but I felt that
τελείωσε πολύ γρήγορα = it finished very quickly

So both:

Η διάρκεια του μαθήματος σήμερα ήταν μία ώρα…
and
Το μάθημα σήμερα κράτησε μία ώρα…

are natural Greek; the first is slightly more formal because of the abstract noun διάρκεια.

How do you pronounce ένιωσα, and what is going on with the νι and ιω there?

ένιωσα is pronounced approximately É-nyo-sa in English transcription.

Syllables: έ-νιω-σα

νι
- ω in νιω produces a nyo sound (like Spanish ño in señor, but a bit lighter).
So νιώ- is pronounced close to nyo: νιώθω ≈ NYO-tho, ένιωσα ≈ É-nyo-sa.

This νι + vowel combination often gives a palatal sound in Greek, which can be tricky for English speakers at first.