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"Confiar" is a transitive verb which is often translated as "to confide", and "fiar" is a transitive verb which is often translated as "to sell on credit". Learn more about the difference between "confiar" and "fiar" below.
confiar(
kohm
-
fyahr
)A transitive verb is a verb that requires a direct object (e.g., I bought a book.).
1. (to tell)
a. to entrust with 
Le confiaron la dirección de la compañía.They entrusted him with the management of the company.
b. to put in charge of 
Estamos buscando a una empresa en quien confiar la realización del proyecto.We're looking for a company to put in charge of the project.
c. to trust 
Muchos jubilados cometieron el error de confiar sus ahorros a esa empresa que ayer quebró.Many pensioners made the mistake of trusting their savings to that company that went under yesterday.
An intransitive verb is one that does not require a direct object (e.g., The man sneezed.).
b. to be confident 
Confío en que van a hacer bien el trabajo.I'm confident that they'll do the job well.
confiarse
A pronominal verb always uses a reflexive pronoun. (e.g., Te ves cansado.).
a. to be overconfident 
No te confíes; este es el primer examen y quedan dos más por aprobar.Don't be overconfident; this is the first exam and there are two more to go.
b. to be too sure of oneself 
Andrea tiene posibilidades de ganar, pero no debería confiarse demasiado.Andrea has chances of winning, but she shouldn't be too sure of herself.
fiar(
fyahr
)A transitive verb is a verb that requires a direct object (e.g., I bought a book.).
a. to sell on credit 
Te fiarán las cervezas si les dices que vas de mi parte.Mention my name and they will sell you the beers on credit.
An intransitive verb is one that does not require a direct object (e.g., The man sneezed.).
a. to give credit 
Ya no fiamos porque tuvimos problemas cobrando a algunos clientes.We no longer give credit because we had difficulties collecting payments.
fiarse
A pronominal verb always uses a reflexive pronoun. (e.g., Te ves cansado.).
a. to trust 
Prefiero darle el dinero directamente a Melisa. No me fío de él.I prefer to give the money straight to Melisa. I don't trust him.
b. to believe 
David prometió que vendría, pero no me fío de sus promesas.David promised he'd come, but I don't believe his promises.