Ο σκύλος είναι μεγάλος και η γάτα είναι μικρή.

Greek definite articles agree with the noun’s grammatical gender, number, and case.

• ο = masculine, nominative, singular → ο σκύλος (the dog)
• η = feminine, nominative, singular → η γάτα (the cat)
• (For reference: το = neuter, nominative, singular)

Adjectives must agree with the noun in gender, number, and case.

• μεγάλος is masculine nominative singular (matches ο σκύλος)
• μικρή is feminine nominative singular (matches η γάτα)

Base forms:

• μεγάλος — μεγάλη — μεγάλο (masc — fem — neut)
• μικρός — μικρή — μικρό

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)

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.

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.”

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.”

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...

• 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.

Put δεν before the verb:

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

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)

Greek sigma has two shapes:

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

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.

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.)