Learn Hardcore Greek: Η λίμνη είναι ήσυχη το πρωί, αλλά το ποτάμι ακούγεται πιο δυνατό. - The lake is quiet in the morning, but the river sounds stronger.

λίμνη is feminine, so it takes the feminine article η (capitalized Η at the start of the sentence).
ποτάμι is neuter, so it takes the neuter article το.

So:

η λίμνη = the lake (feminine)
το ποτάμι = the river (neuter)

The gender is a property of the noun; you simply learn each noun with its article.

Why is it ήσυχη and not ήσυχο after η λίμνη?

Ήσυχη is an adjective meaning “quiet, calm.” In Greek, adjectives must agree in gender, number, and case with the noun they describe.

η λίμνη = feminine singular
So the adjective must also be feminine singular: ήσυχη

If the noun were neuter (e.g. το σπίτι – the house), you’d say:

το σπίτι είναι ήσυχο – the house is quiet

Forms:

masculine: ήσυχος
feminine: ήσυχη
neuter: ήσυχο

Why is it το πρωί for “in the morning”? Why don’t we use a preposition like στο?

Το πρωί literally means “the morning.” In Greek, time expressions often use just the definite article + noun, without a preposition, where English uses “in / on / at.”

So:

το πρωί = in the morning
το βράδυ = in the evening / at night
την Κυριακή = on Sunday

Saying στο πρωί here would be unnatural. You normally use στο with more specific phrases like:

στο πρωινό μάθημα – in the morning class

Can I change the word order and say Το πρωί η λίμνη είναι ήσυχη?

Yes. Greek word order is flexible.

Η λίμνη είναι ήσυχη το πρωί and
Το πρωί η λίμνη είναι ήσυχη

both mean “The lake is quiet in the morning.”

The second version slightly emphasizes “in the morning” (when? in the morning), but grammatically they are both fine and very natural.

What exactly does ακούγεται mean?

Ακούγεται comes from the verb ακούω = “I hear.”
Form: 3rd person singular, present, middle/passive: ακούγεται.

Literally it means “is heard,” “is audible,” but in natural English we usually translate it as “sounds”:

Το ποτάμι ακούγεται πιο δυνατό.
Literally: The river is heard more strong.
Natural English: “The river sounds louder.”

You can think of ακούγεται + adjective roughly like English “sounds + adjective.”

Why is it πιο δυνατό and not πιο δυνατά after ακούγεται?

Greek allows both patterns, but they are slightly different:

ακούγεται πιο δυνατό
- δυνατό is an adjective agreeing with το ποτάμι (neuter singular).
- It describes the river itself as being “more loud/noisy” in character.
- Closer to “the river is louder” / “the river sounds louder.”
ακούγεται πιο δυνατά
- δυνατά here is an adverb = “loudly.”
- Closer to “it is heard more loudly” / “it sounds more loudly.”

In your sentence, πιο δυνατό treats δυνατό as an adjective describing το ποτάμι, so it agrees in gender/number:

το ποτάμι (neuter singular) → πιο δυνατό (neuter singular).

Why does δυνατό end in -ό and not -ός?

The adjective δυνατός, -ή, -ό means “strong, loud.”

Its basic forms:

masculine: δυνατός
feminine: δυνατή
neuter: δυνατό

Since το ποτάμι is neuter singular, the adjective must also be neuter singular:

το ποτάμι είναι δυνατό – the river is loud/strong
το ποτάμι ακούγεται πιο δυνατό – the river sounds louder

If the subject were masculine, you’d say:

ο ήχος είναι δυνατός – the sound is loud

How does the comparative πιο δυνατό work? Is there another way to say “louder / stronger”?

Greek has two main ways to form the comparative of adjectives:

Analytic comparative with πιο
- πιο δυνατό = more strong / louder
  This is very common in modern Greek:
- πιο ήσυχος – quieter
- πιο όμορφη – more beautiful
Synthetic comparative (older / more formal style)
- δυνατό → δυνατώτερο (neuter)
  So you could also say:
- Το ποτάμι ακούγεται δυνατώτερο.
  (Correct but sounds more formal/literary.)

In everyday speech, πιο δυνατό is by far the usual choice.

Why is there a comma before αλλά?

Αλλά means “but.” In Greek, it usually connects two clauses and is normally preceded by a comma, just like “but” often is in English.

Η λίμνη είναι ήσυχη το πρωί, αλλά το ποτάμι ακούγεται πιο δυνατό.

This comma separates:

Η λίμνη είναι ήσυχη το πρωί – the lake is quiet in the morning
το ποτάμι ακούγεται πιο δυνατό – the river sounds louder

So the comma + αλλά together express a clear contrast.

Why do we need the article again in το ποτάμι after αλλά? Could we drop it?

You normally keep the article:

…αλλά το ποτάμι ακούγεται πιο δυνατό.

In Greek, definite nouns almost always keep their article, even when a similar noun has already been mentioned. Omitting the article (…αλλά ποτάμι ακούγεται…) would sound incorrect here.

Compare:

Μου αρέσει η λίμνη, αλλά το ποτάμι είναι πιο όμορφο.
I like the lake, but the river is more beautiful.

Greek uses the definite article more consistently than English; don’t be afraid to repeat it.

How are λίμνη, είναι, and ήσυχη pronounced, especially the η, ι, and ει?

All of η, ι, ει are pronounced as the same sound, like the English “ee” in see.

Approximate pronunciations:

λίμνη → LÍM-ni
- stress on the first syllable
- η at the end is not a separate “ee” syllable; it just affects spelling and stress.
είναι → Í-ne
- ει = “ee,” so it sounds like íne
ήσυχη → Í-si-chi
- ή = “ee,” stressed;
- χ is a voiceless sound like the ch in German Bach or Scottish loch.

Stress marks (´) show which syllable is stressed, and that is important in Greek.

Why is it είναι and not είναι είναι or something else for “is”? What form is this?

Είναι is the present tense of “to be” used for he / she / it / they:

είμαι – I am
είσαι – you are (singular)
είναι – he / she / it is; they are

In Η λίμνη είναι ήσυχη,

subject: η λίμνη (the lake, “it”)
verb: είναι (is)

So η λίμνη είναι = “the lake is.” You don’t repeat είναι; one verb is enough.

Does είναι here mean something happening right now, or a general fact?

Greek present tense (like είναι) can express both:

a general fact / habit, and
something currently true.

In this sentence, it most naturally describes a general situation:

Η λίμνη είναι ήσυχη το πρωί
= The lake is (generally) quiet in the morning (as a usual pattern).

If you wanted to talk about a specific past morning, you might instead use the past:

Η λίμνη ήταν ήσυχη το πρωί. – The lake was quiet in the morning.