Les?

Les juro que guardaré su secreto.

(I) swear that (I) will keep your secret.

from 14.7

Why is it ‘les' and not ‘le’

or les and sus?

¡Hola TravisB13!

I'll break this down into sections!

1. Why les?

In this sentence, the speaker is addressing more than one person using the plural ustedes “you (plural)” form - this is why they use the plural indirect object pronoun les. If they had used le instead, then they would be addressing just one person using the singular usted “you (formal)” form.

2. Why su?

The ustedes “you (plural)” form has two possible short-form possessive adjectives (i.e. words for “your”): su and sus. Don't forget that in Spanish, possessives reflect the number of the thing being owned, rather than the number of the person doing the owning. So because the thing being owned here (el secreto “the secret”) is singular, the speaker uses the singular su. They would only use the plural sus if there were more than one secret being owned.

I hope that this is helpful! If you'd like a little review on possessives in Spanish, you can find a full explanation in Lesson 4.8: "Talking About 'Yours' and 'Mine.'" And if you have any further questions, just let me know!

Saludos,

Liss