Su hermano no es antipático; simplemente es menos sociable y habla poco al principio.

Because su is a possessive adjective, meaning something like his/her/your/their depending on context. In Spanish, a possessive usually replaces the article.

So you say:

• su hermano = his/her/your/their brother
• not el su hermano in standard modern Spanish

This is different from English, where we also do not say the his brother.

Su can mean several things:

• his
• her
• your (formal singular, usted)
• their
• sometimes your (plural, in many Latin American varieties)

So Su hermano is grammatically ambiguous on its own. You need context to know whose brother it is.

If Spanish speakers want to make it clearer, they can add:

• el hermano de él
• el hermano de ella
• el hermano de usted
• el hermano de ellos

Spanish usually uses ser for more lasting or characteristic qualities, and estar for temporary states or conditions.

Here, antipático and sociable describe personality traits, so ser is the natural choice:

• es antipático
• es menos sociable

If you used está here, it would sound unusual unless you were talking about a temporary attitude in a very specific context.

So the sentence presents this as part of his general personality, not just how he happens to be today.

Not exactly. This is a very common false friend.

In Spanish, antipático usually means:

• unfriendly
• unpleasant
• not nice
• rude/stand-offish depending on context

It does not usually mean English antipathetic.

So in this sentence, no es antipático means he is not an unpleasant or unfriendly person.

Because it agrees with hermano, which is masculine singular.

Spanish adjectives usually agree in gender and number with the noun they describe:

• hermano antipático
• hermana antipática
• hermanos antipáticos
• hermanas antipáticas

Here, hermano is masculine singular, so the adjective is antipático.

Simplemente means simply or just here. It softens and clarifies the statement.

The idea is:

• he is not unfriendly;
• rather, the explanation is that he is less sociable and does not talk much at first.

So simplemente helps contrast appearance and reality. It sounds like:

• He’s not rude; he’s just less sociable...

Because menos sociable means less sociable, which is softer and more nuanced than saying someone is not sociable.

Compare:

• no es sociable = he is not sociable
• es menos sociable = he is less sociable

The second one is more relative and less absolute. It suggests he may still be sociable, just not as much as other people or not in every situation.

Yes, but it changes the structure slightly.

• menos sociable = less sociable
• no tan sociable = not as sociable

Both are correct, but menos sociable is the direct comparative form. It is a neat, natural choice here.

For example:

• Es menos sociable que su hermana = He is less sociable than his sister.
• No es tan sociable como su hermana = He is not as sociable as his sister.

Habla poco is the normal word order in Spanish: verb + adverb/quantity expression.

• habla poco = he talks little / he doesn’t talk much

You can sometimes move poco for emphasis in special contexts, but poco habla would sound marked, poetic, or unusual in everyday speech.

So for a neutral statement, habla poco is the standard form.

Usually no. Habla poco means he doesn’t talk much or he says little.

It refers to the amount he speaks, not the volume of his voice.

If you wanted to say he speaks quietly/softly, you would normally use something like:

• habla en voz baja
• habla bajito

So here the meaning is about being reserved, not about speaking softly.

Al principio means at first or in the beginning.

In this sentence, it means that when he first meets people or first enters a situation, he does not talk much. The idea is that this may change later, once he becomes more comfortable.

So:

• habla poco al principio = he doesn’t say much at first

Because a + el contracts to al in Spanish.

So:

• a + el = al

That is why you get:

• al principio

This contraction is required except when el is part of a proper name, such as a El Escorial.

The semicolon links two closely related ideas:

• Su hermano no es antipático
• simplemente es menos sociable y habla poco al principio

It shows a stronger pause than a comma, but a closer connection than a full stop.

In English, this works similarly. The second part explains or qualifies the first one.

You could also write it with a full stop in many contexts, but the semicolon makes the relationship especially clear.

In Spanish, the negative word no normally goes directly before the conjugated verb.

So:

• no es = is not
• no habla = does not speak

That is why the sentence says:

• Su hermano no es antipático

This is the standard way to negate a verb in Spanish.

Yes, you could say:

• Su hermano no es antipático, pero simplemente es menos sociable y habla poco al principio.

However, this version is slightly less elegant, because simplemente already introduces the explanation. The original punctuation is smoother and avoids over-connecting the ideas.

A very natural alternative would be:

• Su hermano no es antipático; es simplemente menos sociable y habla poco al principio.

No, they are different.

• al principio = at first / at the beginning
• en principio = in principle / theoretically

So in this sentence, al principio is the correct choice, because it refers to the initial stage of meeting people or starting an interaction.

Yes, that is a very natural English translation. It is not a word-for-word translation, but it expresses the same idea well.

Literally, it means:

• he talks little at first

But in natural English, he is quiet at first often sounds better.

That kind of translation is common when moving from Spanish structure to natural English phrasing.