Learn Hardcore Greek: Ο καφές σήμερα είναι πολύ γλυκός.

Ο καφές = the coffee (a specific coffee you’re drinking now)
Just καφές (without ο) is more like talking about coffee in general, or in some fixed expressions.

In this sentence we mean this particular coffee today, so Greek uses ο καφές with the article ο (masculine, singular, nominative).

Why is the article ο and not το or η?

Greek nouns have grammatical gender: masculine, feminine, or neuter.

ο = the (masculine nominative singular)
η = the (feminine nominative singular)
το = the (neuter nominative/accusative singular)

The word καφές (coffee) is masculine, so it takes the masculine article ο:

ο καφές = the coffee

What case is ο καφές, and why?

Ο καφές is in the nominative case.

In Greek:

The nominative case is used for the subject of the sentence.
Here, ο καφές is the subject: it’s the thing that “is very sweet”.

So ο καφές must be nominative masculine singular: ο καφές.

What does σήμερα mean, and where can it go in the sentence?

σήμερα means today.

In Greek, adverbs of time like σήμερα are flexible in position. All of these are correct and natural:

Ο καφές σήμερα είναι πολύ γλυκός.
Σήμερα ο καφές είναι πολύ γλυκός.
Ο καφές είναι πολύ γλυκός σήμερα.

The meaning is the same: the coffee today is very sweet. Word order changes emphasis, not the basic meaning. For example, starting with Σήμερα lightly emphasizes “today”.

What form of the verb is είναι, and why is it used here?

είναι is the third person singular, present tense of the verb είμαι (to be).

Forms of είμαι (present):

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

Here the subject is ο καφές (he/it), so we use είναι = is:

Ο καφές … είναι … = The coffee … is …

Why is πολύ and not πολύς used here?

Greek distinguishes between:

πολύς / πολλή / πολύ (adjectives) = much, many (agree in gender/number/case with a noun)
πολύ (invariable adverb) = very, a lot (goes with adjectives, adverbs, or verbs)

In this sentence πολύ modifies the adjective γλυκός:

πολύ γλυκός = very sweet

Here πολύ is an adverb, so it does not change form; it stays πολύ regardless of gender or number of the noun.

Why is the adjective γλυκός (masculine) and not something like γλυκό or γλυκή?

Adjectives in Greek must agree with the noun they describe in:

Gender (masculine / feminine / neuter)
Number (singular / plural)
Case (nominative / accusative / etc.)

The noun is:

ο καφές → masculine, singular, nominative

So the adjective must also be:

masculine, singular, nominative → γλυκός

Other forms:

γλυκός = sweet (masc. nom. sg.)
γλυκή = sweet (fem. nom. sg.)
γλυκό = sweet (neuter nom./acc. sg.)

Since καφές is masculine, we choose γλυκός.

Is πολύ γλυκός closer to “very sweet”, “too sweet”, or “so sweet”?

Literally, πολύ γλυκός means very sweet.

Depending on tone and context, it can feel like:

very sweet (neutral/intensifying)
sometimes too sweet (if said with a complaining tone)

If you want to clearly say too sweet, you can use:

υπερβολικά γλυκός = excessively sweet, too sweet

But in everyday speech, people often use πολύ γλυκός with intonation to mean “too sweet”.

Could the verb είναι be left out, like in some other languages?

In modern Greek, you cannot normally drop the verb είναι in the present tense the way you can in Russian/Arabic, etc.

So:

Ο καφές σήμερα πολύ γλυκός ❌ (incorrect)
Ο καφές σήμερα είναι πολύ γλυκός. ✅ (correct)

You can drop subject pronouns (like “I”, “you”, etc.), but you keep the verb.

Why is the subject (ο καφές) explicit? Could it be omitted?

Here, ο καφές names a specific thing (the coffee), so you need it; there is no pronoun to replace:

Είναι πολύ γλυκός. = He/it is very sweet.
This is grammatically fine but unclear without context.

If everyone already knows you’re talking about the coffee, you might say just:

Είναι πολύ γλυκός. (“It’s very sweet.”)

But in a neutral, clear sentence — especially in a learning context — we include ο καφές.

How is καφές pronounced, and what do the accent marks mean?

Pronunciation: καφές = ka-FES

κα → “ka” (like cut but with a clearer “a”)
φ → “f”
The accent on ές shows the stressed syllable: ka-FES

Greek uses an accent mark (´) to show the stressed syllable in words of more than one syllable.
In this sentence:

καφές → stress on -φές
σήμερα → ΣΉ-με-ρα (stress on -σή-)
είναι → ΕΊ-νε (stress on -εί-)
γλυκός → γλυ-ΚΌΣ (stress on -κός)

Stress is phonemic in Greek; changing it can change the meaning or make the word sound wrong.

Could this sentence also mean “The coffee today is very sweet” as opposed to other days?

Yes. σήμερα naturally carries the idea of “today (as opposed to other times)”.

So:

Ο καφές σήμερα είναι πολύ γλυκός.

Can be understood as:

The coffee today is very sweet (implying that it might not always be this sweet).

If you really wanted to emphasize the contrast, you could say:

Σήμερα ο καφές είναι πολύ πιο γλυκός.
= Today the coffee is much sweeter (than usual).