Learn Hardcore Greek: Ο σκύλος είναι μεγάλος και η γάτα είναι μικρή.

It’s the 3rd person form of the verb είμαι (to be). It serves as both “he/she/it is” and “they are”; the subject tells you which. Present tense for reference:

είμαι (I am), είσαι (you are), είναι (he/she/it is)
είμαστε (we are), είστε/είσαστε (you are), είναι (they are)

What case are the nouns and adjectives in?

Nominative. Subjects take nominative (ο σκύλος, η γάτα), and after the verb είμαι (to be), the predicative adjective also stays in the nominative (μεγάλος, μικρή).

Can I drop the second είναι?

Yes. Greek often omits a repeated verb:

Ο σκύλος είναι μεγάλος και η γάτα μικρή. This is natural. Don’t drop the first είναι here.

Can I put the adjectives before the nouns?

Yes, but the meaning changes.

Ο σκύλος είναι μεγάλος = “The dog is big” (predicate)
Ο μεγάλος σκύλος = “The big dog” (attributive; describes which dog)
Similarly: η μικρή γάτα = “the small cat.”

How do I pronounce the sentence?

A simple guide with stressed syllables in caps:
o SKÍ-los Í-ne me-GÁ-los ke i GÁ-ta Í-ne mi-KRÍ

Notes:

γ before α/ο/ου sounds like a soft voiced “gh” (as in Spanish “amigo”): γάτα ≈ “GHA-ta.”
η, υ, ι, ει, οι are all pronounced “ee.”
και is pronounced “ke.”

Why doesn’t the article η have an accent, but είναι does?

Monosyllabic function words like the article η are normally unaccented. είναι has two syllables and carries a stress accent on its first syllable. (A common accented monosyllable to contrast is ή = “or.”)

What does και mean, and can it be κι?

και means “and” (pronounced “ke”). Before a vowel sound it’s often written κι for smoother flow (e.g., κι εγώ = “and I”), but both forms mean “and.”

Do I need the articles here? Could I say “Σκύλος είναι μεγάλος ...”?

Use the definite article with subject nouns in standard Greek, even for general statements.

Ο σκύλος είναι... sounds natural.
Σκύλος είναι... is odd.
For “a dog,” use the indefinite article: Ένας σκύλος...

How do I say this in the plural?

Οι σκύλοι είναι μεγάλοι και οι γάτες είναι μικρές.
- οι = plural definite article (masc/fem nominative)
- Adjectives: μεγάλοι (masc pl), μικρές (fem pl)

Common alternative with the neuter word for “dog”:

Τα σκυλιά είναι μεγάλα.

How do I negate it?

Put δεν before the verb:

Ο σκύλος δεν είναι μεγάλος και η γάτα δεν είναι μικρή.

Are σκύλος and γάτα always masculine/feminine? What if I want to specify sex?

They have fixed grammatical genders: σκύλος (masc), γάτα (fem). To specify sex:

Female dog: η σκύλα
Male cat: ο γάτος
Common everyday term for “dog” (neuter): το σκυλί (plural τα σκυλιά)

Why does the final σ look different in σκύλος?

Greek sigma has two shapes:

σ inside a word
ς at the end of a word
So σκύλος ends with ς.

Is the word order fixed?

The neutral order is Subject–Verb–Predicate: Ο σκύλος είναι μεγάλος. Greek allows flexibility for emphasis:

Μεγάλος είναι ο σκύλος (emphasizes “big”).
Agreement via articles and endings keeps the meaning clear.

How do I say “bigger/smaller” with these words?

Use comparative/superlative forms:

μεγαλύτερος/μεγαλύτερη/μεγαλύτερο = bigger
μικρότερος/μικρότερη/μικρότερο = smaller Example: Ο σκύλος είναι μεγαλύτερος από τη γάτα. (The dog is bigger than the cat.)