Learn Hardcore Spanish (Spain): Mi hermano estudia mucho en la biblioteca.

mi = my (a possessive adjective, used before a noun)
- mi hermano = my brother
- mi casa = my house
me = me (an object pronoun, used before/after verbs)
- Él me ayuda. = He helps me.
- Me llamo Ana. = My name is Ana.

Because you’re saying my brother, you must use the possessive mi, not the pronoun me.

Why is there no article before mi hermano? Why not el mi hermano?

With possessive adjectives like mi, tu, su, nuestro, Spanish does not use an article:

mi hermano = my brother
tu hermana = your sister
nuestros amigos = our friends

Using an article plus a possessive (el mi hermano) is incorrect in standard Spanish. The article is only used if you replace the possessive with a de-phrase:

el hermano de Juan = Juan’s brother
la hermana de María = María’s sister

Does mi hermano always mean “my brother,” or can it also mean “my sibling”?

Literally, hermano is brother and hermana is sister.

mi hermano = my brother
mi hermana = my sister

However, hermano/hermana can sometimes be used more generically for a sibling, especially in contexts where gender isn’t important, but normally if you know the gender you choose hermano or hermana.

If you want to refer to siblings in general, you say:

mis hermanos = my siblings / my brothers (could include sisters)

Why is it estudia and not estudio or estudian?

Spanish verbs change form depending on who is doing the action. For estudiar (to study), the present tense is:

yo estudio = I study
tú estudias = you (informal) study
él / ella / usted estudia = he / she / you (formal) study
nosotros estudiamos = we study
vosotros estudiáis = you (plural, Spain) study
ellos / ellas / ustedes estudian = they / you (plural, Latin America) study

The subject is mi hermano = he.
So you must use the 3rd person singular form: estudia.

Why does Spanish use estudia (simple present) instead of something like “is studying,” like in English?

Spanish simple present (estudia) can cover several meanings that English separates:

Mi hermano estudia mucho.
- He studies a lot.
- He is studying a lot (these days / in general).

If you really want to stress “right now,” Spanish can also use the present progressive:

Mi hermano está estudiando en la biblioteca. = My brother is studying in the library (right now).

But in many cases where English says “is studying”, Spanish is perfectly natural with just estudia.

Why is mucho placed after estudia? Could I say Mi hermano mucho estudia?

With verbs, mucho usually goes after the verb:

estudia mucho = studies a lot
trabaja mucho = works a lot
come mucho = eats a lot

Putting mucho before the verb (mucho estudia) is either wrong or sounds very marked/poetic in modern Spanish. The normal, everyday word order is:

Mi hermano estudia mucho. ✔️

What is the difference between mucho and muy? Could I say estudia muy?

They are not interchangeable:

mucho modifies verbs and nouns:
- Verb: Estudia mucho. = He studies a lot.
- Noun: Tiene mucho trabajo. = He has a lot of work.
muy modifies adjectives and adverbs:
- Adjective: Es muy inteligente. = He is very intelligent.
- Adverb: Corre muy rápido. = He runs very fast.

So:

Estudia mucho. ✔️ (correct)
Estudia muy. ✘ (incorrect; you’d need an adjective or adverb after muy)

Why is it en la biblioteca and not something like a la biblioteca?

In Spanish:

en usually means in / on / at (location)
a usually means to (direction/motion)

In this sentence, the idea is where he studies, not where he’s going:

Mi hermano estudia mucho en la biblioteca.
= He studies a lot in/at the library.

If you wanted to express movement, you would use a:

Mi hermano va a la biblioteca. = My brother goes to the library.

Why is it la biblioteca and not just biblioteca, like in English “at library”?

Spanish normally uses a definite article with singular countable nouns, where English often omits it:

en la biblioteca = in the library
en la escuela = at school
en el trabajo = at work

So you generally say:

en la biblioteca, not en biblioteca.

You could use una biblioteca if you mean a library in the sense of “some (unspecified) library”:

Estudia en una biblioteca cerca de su casa. = He studies in a library near his house.

Why do we say la biblioteca and not el biblioteca?

Every Spanish noun has a grammatical gender, masculine or feminine.
biblioteca is feminine, so it takes the feminine article la:

la biblioteca = the library

Other examples:

el libro (masculine) → el libro nuevo = the new book
la mesa (feminine) → la mesa nueva = the new table

Because biblioteca ends in -a and is feminine, you must say la biblioteca, not el biblioteca.

Why is there no él in the sentence? Could I say Mi hermano él estudia mucho en la biblioteca?

Spanish often omits subject pronouns (yo, tú, él, etc.) when the subject is clear from context or from the verb form.

Here, the subject is already in the sentence: mi hermano.
Adding él would be redundant and sound wrong:

Mi hermano estudia mucho… ✔️
Él estudia mucho en la biblioteca. ✔️ (if you just say “He studies…”)
Mi hermano él estudia mucho… ✘ (unnatural / incorrect in standard Spanish)

You use él when the subject is not otherwise expressed or when you want to emphasize/contrast:

Él estudia mucho, pero su amigo no. = He studies a lot, but his friend doesn’t.

Why doesn’t mi have an accent, but sometimes I see mí with an accent?

They are different words:

mi (no accent) = my (possessive adjective)
- mi hermano, mi casa, mi libro
mí (with accent) = me (stressed object pronoun after prepositions)
- para mí = for me
- a mí = to me
- sin mí = without me

In Mi hermano estudia mucho en la biblioteca, you need mi = my, so no accent.

How would the sentence change if I talked about several brothers?

You have to make both the possessive and the noun plural, and adjust the verb:

Mis hermanos estudian mucho en la biblioteca.
- mis = my (plural)
- hermanos = brothers / siblings
- estudian = they study (3rd person plural form of estudiar)

So:

Mi hermano estudia… = My brother studies…
Mis hermanos estudian… = My brothers / My siblings study…