Αυτός είναι ο αδερφός μου.

to be

Breakdown of Αυτός είναι ο αδερφός μου.

• μου: my
• ο αδερφός: the brother
• αυτός: it

Questions & Answers about Αυτός είναι ο αδερφός μου.

Why does the sentence start with Αυτός? Could you just say Είναι ο αδερφός μου?

Αυτός means this (man) or he and is the subject of the sentence.

• Αυτός είναι ο αδερφός μου = This is my brother / He is my brother.
• Είναι ο αδερφός μου = He is my brother (more like He’s my brother, without pointing or strong emphasis).

In Greek, subject pronouns (like αυτός, αυτή, εγώ, εσύ) are often dropped because the verb ending already shows the person.
You keep Αυτός when you:

• want to point someone out (this one here is my brother), or
• want to contrast or emphasize (He is my brother (not someone else)).

So yes, you can say Είναι ο αδερφός μου, but it slightly changes the feel: less pointing, more simple statement.

Why is it Αυτός (masculine) and not Αυτή or Αυτό?

Greek demonstrative pronouns agree in gender with the person or thing you are referring to.

• Αυτός = this man/he (masculine)
• Αυτή = this woman/she (feminine)
• Αυτό = this thing/it or this child (neuter)

Because αδερφός (brother) is a masculine noun, you use the masculine form Αυτός.

If you were saying This is my sister, you would say:

• Αυτή είναι η αδερφή μου.

What is the function of είναι in this sentence?