Learn Hardcore Greek: Ο καφές είναι ζεστός, αλλά το νερό είναι κρύο. - The coffee is hot, but the water is cold.

ο = masculine nominative singular (as in ο καφές)
το = neuter nominative singular (as in το νερό) Both nouns are subjects here, so the nominative case is used.

Why does ζεστός end in -ος but κρύο end in -ο?

Adjectives agree with the noun’s gender, number, and case.

καφές is masculine → masculine adjective ζεστός
νερό is neuter → neuter adjective κρύο Typical patterns:
ζεστός (m), ζεστή (f), ζεστό (n)
κρύος (m), κρύα (f), κρύο (n)

How do I know the genders of καφές and νερό?

Learn nouns with their article: ο καφές (masc), το νερό (neut). Heuristics help (many nouns in -ς are masculine; many in -ο are neuter), but there are exceptions, so the article is your safest guide.

Is είναι the verb “to be”? Which form is it?

Yes. είναι is the present tense of είμαι, used for both third-person singular and plural.

Present: είμαι, είσαι, είναι, είμαστε, είστε/είσαστε, είναι In this sentence each είναι is “is” because the subject is singular.

Do I need the second είναι, or can I write Ο καφές είναι ζεστός, αλλά το νερό κρύο?

In normal speech and writing you repeat είναι: ..., αλλά το νερό είναι κρύο. Omitting it is acceptable mainly in headlines or very telegraphic style.

What does αλλά mean, and is the comma before it necessary?

αλλά means “but.” Use a comma when it links two independent clauses, as here. If it links shorter phrases, the comma can be omitted. You can also use μα (colloquial/expressive “but”) in the same spot.

Why can’t I say Το νερό είναι κρύος?

Because adjectives must agree with the noun. νερό is neuter, so the adjective must be neuter: κρύο (not masculine κρύος). Similarly: η σούπα είναι κρύα (feminine).

Where do adjectives go in Greek—before or after the noun?

Predicate position (statement about the noun): Ο καφές είναι ζεστός.
Attributive position (modifies the noun): Ο ζεστός καφές = “the hot coffee.” You can also say ο καφές ο ζεστός (more formal/emphatic). If you put the adjective before the noun without an article, it’s predicative: Ζεστός είναι ο καφές.

Is κρύο here an adjective or a noun?

An adjective (“is cold”). As a noun, το κρύο means “the cold” (cold weather). Common weather expressions: Κάνει κρύο / Έχει κρύο = “It’s cold (outside).”

How do I pronounce the key words?

είναι (íne) = EE-neh, stress on the first syllable
ζεστός (zestós) = zeh-STOS
κρύο (krío) = KREE-oh (two syllables)
ο καφές (o kafés) = ka-FES
το νερό (to neró) = ne-RO
αλλά (allá) = a-LA

Are there stronger or weaker words than ζεστός and κρύος?

Yes:

Hot scale: χλιαρός (lukewarm) < ζεστός (warm/hot) < καυτός (very hot/scalding)
Cold scale: δροσερός (cool) < κρύος (cold) < παγωμένος (icy) Pick based on intensity and context.

Can I change the word order for emphasis?

Yes. Greek allows fronting: Ζεστός είναι ο καφές, αλλά κρύο είναι το νερό. Same meaning, with emphasis on the adjectives. You can also use όμως (“however”): Ο καφές είναι ζεστός, το νερό όμως είναι κρύο.

How would this look in the plural?

Nouns: ο καφές → οι καφέδες, το νερό → τα νερά
Adjectives: ζεστός → ζεστοί (masc pl), κρύο → κρύα (neut pl) Full sentence: Οι καφέδες είναι ζεστοί, αλλά τα νερά είναι κρύα. Note: τα νερά is used for bottles/types of water or bodies of water; ordinary drinking water is typically singular το νερό.

Could I say “a coffee” or “a water” instead of using the definite article?

ένας καφές = “a coffee” (countable drink order)
For water, Greek often drops the article for an unspecified amount: Θέλω νερό = “I want water.” Use ένα νερό when you mean a unit (a bottle/glass): Ένα νερό, παρακαλώ.

Why does the first word Ο have no accent mark?

Because it’s the definite article. The articles ο, η, το are monosyllabic and written without a tonos. Capital letters normally keep the accent when needed (e.g., Όχι), but Ο as an article never takes one.