Learn Hardcore Spanish (Latin America): En otoño las hojas caen al río y lo decoran con colores. - In autumn the leaves fall into the river and decorate it with colors.

In Spanish, seasons are often mentioned without a definite article when speaking generally. So you say en otoño, en primavera, en verano, etc. You can use en el otoño to emphasize a specific autumn, but for general statements it’s more natural to omit the article.

What does al mean in caen al río, and why don’t we write a el río?

Al is simply the contraction of a (to) + el (the). Spanish grammar requires you to combine them into al instead of writing a el separately.

What tense is caen, and why is the present tense used here?

Caen is the third-person plural present indicative form of caer (to fall). Spanish—like English—uses the present tense to express habitual actions or general truths. Here it describes what usually happens in autumn.

Why do we use lo in lo decoran, and what does it refer to?

Lo is the masculine singular direct-object pronoun “it.” It replaces el río to avoid repeating the noun. So lo decoran con colores literally means “they decorate it with colors.”

Why is colores plural, and could we use color instead?

Since the leaves bring multiple hues, Spanish uses the plural colores. Using color would sound abstract, like referring to “color” in general, not to the specific variety of colors decorating the riverbank.

Why isn’t there a comma before y lo decoran?

In Spanish, you don’t place a comma before y when it simply joins two verbs that share the same subject. Here caen and decoran both refer back to las hojas, so no comma is needed.

Is decorar here a literal painting, or is it figurative?

It’s figurative. Decorar means “to decorate,” so the sentence suggests that the leaves “decorate” the river with their colors. Saying pintan (they paint) would imply a deliberate act of painting, which isn’t intended.