Short forms before nouns (buen, primer, algún, ningún)

un buen libro, el primer díaa good book, the first day

A handful of common Spanish adjectives drop their final -o the moment they land right before a masculine singular noun phrase. This shortening is called apocopation, and once you know the small list of words it applies to, the pattern itself is simple.

Quick shortcut: bueno → buen, malo → mal, primero → primer, tercero → tercer, alguno → algún, ninguno → ningún, uno → un — all only before a masculine singular noun (with or without another word in between). grande → gran is the one exception that shortens before any singular noun, masculine or feminine.

The core pattern: drop the -o before a masculine singular noun

These adjectives shorten when they come before a masculine singular noun — most often right next to it, but another modifier can also sit in between: algún otro problema (some other problem), ningún buen amigo (no good friend), el primer gran paso (the first great step). Elsewhere — after the noun, before a feminine or plural noun, or standing alone — they keep their full form:

alguno and ninguno work the same way — shortening to algún and ningún right before a masculine singular noun — and already have their own lesson: Basic indefinite words.

• ¿Tienes algún problema? (Do you have any problem?) — but alguna pregunta, algunos libros
• No tengo ningún interés. (I have no interest.) — but ninguna duda

uno shortens to un the same way — but this is really just the indefinite article you already know from Indefinite articles: un libro, never ❌ uno libro.

Grande → gran: the exception that covers both genders

grande is different from the rest of the list in one key way: it shortens to gran right before any singular noun — masculine or feminine — not just masculine ones. The meaning often shifts too: gran before the noun usually means "great," while grande after the noun more often refers to size — though the postnominal form can carry other context-dependent meanings too (un hombre grande can mean a big man, or simply a grown man, depending on context):

• un gran hombre (a great man) vs. un hombre grande (a big man)
• una gran mujer (a great woman) vs. una mujer grande (a big woman)

In the plural, grande never shortens: grandes hombres, grandes mujeres.

Ciento → cien, and santo → san

Two more common words shorten too, each with its own small twist:

• ciento shortens to cien right before a noun, or before mil or millón/millones (cien libros, cien mil, cien millones) — but not before a smaller number added to it, like ciento uno or ciento veinte (101, 120), even though 101 and 120 are themselves larger than 100. This has its own detailed coverage in Using and omitting articles.
• santo shortens to san right before most saints' names: San Pedro, San Francisco. The main exceptions are names starting with To- or Do-, which keep the full form: Santo Tomás, Santo Domingo.

Common mistakes

• ✅ un libro bueno is fine after the noun; but ❌ un bueno libro → ✅ un buen libro before it
• ❌ la primer vez → ✅ la primera vez (no shortening before a feminine noun)
• ❌ un gran libros → ✅ unos grandes libros (grande never shortens in the plural)
• ❌ San Tomás → ✅ Santo Tomás (names starting with To-/Do- keep the full form)

Quick check

Choose the correct form:

1. Hoy es un (bueno/buen) día.
2. Es la (primer/primera) clase del día.
3. Einstein fue un (gran/grande) científico.
4. No tengo (ninguno/ningún) problema.
5. Vinieron (cien/ciento) personas.

Key takeaways

• bueno/malo/primero/tercero/alguno/ninguno/uno drop their final -o only before a masculine singular noun (often right next to it, but another word can sit in between): buen, mal, primer, tercer, algún, ningún, un.
• grande is the exception: it shortens to gran before any singular noun, masculine or feminine, and never shortens in the plural.
• ciento shortens to cien before a noun or a larger number; santo shortens to san before most names, except those starting with To-/Do- (Santo Tomás, Santo Domingo).
• Outside that one position — after the noun, before a feminine noun, before a plural, or standing alone — every one of these words keeps its full form.