How do Spanish object pronouns work?
Direct object pronouns — lo, la, los, las — replace the thing being acted on. Indirect object pronouns — le, les — replace the person receiving it. They go before a conjugated verb, or attach to the end of an infinitive, gerund or command. When both appear together, the indirect one comes first and le turns into se.
Direct against indirect
The direct object is what the verb happens to. The indirect object is who ends up with it. In I gave the book to Maria, the book is direct and Maria is indirect. Spanish marks the difference in the pronoun, which English does not, so the distinction has to be made consciously at first.
Veo el libro. → Lo veo.
I see the book. → I see it.
Veo a María. → La veo.
I see María. → I see her.
Le doy el libro.
I give him/her the book.
Le is the recipient.
Where they go
Before a conjugated verb, always — Spanish does not put them after it the way English does. With an infinitive or a gerund you have a genuine choice: put the pronoun before the whole construction or attach it to the end. Both are correct and both are common. With affirmative commands attachment is compulsory.
Lo quiero comer. / Quiero comerlo.
I want to eat it.
Both correct.
Lo estoy leyendo. / Estoy leyéndolo.
I'm reading it.
¡Cómelo!
Eat it!
Attached — commands leave no choice.
Le becomes se
When an indirect and a direct pronoun appear together, the indirect comes first — and if it is le or les, it changes to se. This is purely about sound: Spanish avoids le lo, so it substitutes se. It is not reflexive here despite looking identical to the reflexive pronoun.
Se lo di.
I gave it to him.
Not le lo di.
¿Se las mandaste?
Did you send them to her?
Common mistakes
Le veo.
Lo veo. / La veo.
Seeing someone takes a direct object. Le for a person you see is leísmo — widespread in parts of Spain and accepted there for masculine people, but not the neutral standard.
Le lo di.
Se lo di.
Le before lo is not allowed; it becomes se.
Quiero lo comer.
Quiero comerlo. / Lo quiero comer.
The pronoun goes before the conjugated verb or attaches to the infinitive — never loose in between.
Frequently asked questions
What is leísmo and should I copy it?
Using le where standard grammar wants lo, mainly for masculine people — le vi rather than lo vi. It is normal in central and northern Spain and the Real Academia accepts it for masculine singular persons. If you are learning Latin American Spanish, use lo.
Why does Spanish repeat the object — le di el libro a Juan?
Because the indirect pronoun is usually obligatory even when the full noun is also present. It looks redundant to an English speaker and is simply required; leaving out le there sounds wrong.
Do the pronouns change with the verb?
No, they change with what they replace — gender and number of the object, not the subject. La in la veo tells you the thing seen is feminine and singular, and nothing about who is doing the seeing.