Using object pronouns le/la/les vs lui/leur in affirmative commands in the imperative mood (L'Impératif) in French

Look at these sentences in L'Impératif:

Note that in L'Impératif, the direct object pronouns le, la, l', les and the indirect object pronouns lui, leur are placed after the verb with a hyphen in between.


ATTENTION:
It's often very confusing for students to know which pronoun to use in affirmative commands.

Look at these two examples:

Nous écrivons à notre tante -> Nous lui écrivons -> Écrivons-lui !
We're writing to our aunt -> We write to her -> Let's write to her!

BUT

Tu arrêtes Paul -> Tu l'arrêtes -> Arrête-le !
You're stopping Paul -> You're stopping him -> Stop him!

Here is the rule:

- If the verb is normally followed by à+ personin French (i.e., followed by an indirect object pronoun),such as in écrire à [quelqu'un] (to write to [someone]) or montrer à [quelqu'un](to show [someone]), then you use lui or leur.

- If the verb isn't followed by any preposition (i.e. followed by a direct object pronoun), such as arrêter [X] [quelqu'un](to stop [someone]), you use le/la or les.

See also Using le/la/l'/les = it/him/her/them (French Direct Object Pronouns) and Using lui/leur = him or her/them (French Indirect Object Pronouns)

Special cases
Look at these examples:

Note that quite a few verbs, such as regarder and attendre, are used without prepositions in French, i.e., regarder [x] [quelqu'un]; attendre [x] [quelqu'un], whereas they have one in English (i.e., to look at [someone], to wait for [someone]).

On the other hand, some English verbs without prepositions will be followed by à in French, i.e., to phone [someone] = téléphoner à [quelqu'un].

When in doubt, check with a dictionary.

See also Conjugate regular verbs in the imperative mood in French (L'Impératif) and Conjugate irregular être/avoir/savoir in the imperative mood in French (L'Impératif)