credo

Credo, credere, credidi, creditum is a third conjugation verb, and like do it has the old reduplicated perfect: credidi.

The construction is the whole lesson. The person or thing you TRUST goes into the DATIVE, tibi credo, "I believe you", nemo ei credidit, "nobody trusted him". The proposition you believe goes into an accusative and infinitive, credo eum venire, "I believe that he is coming". Put a person in the accusative after credo and you have said something different and probably ungrammatical. It belongs to a small family: credo, faveo, noceo, parco, pareo, persuadeo, studeo and the rest of the dative verbs, which take a dative where English expects a direct object.

Its other sense is commercial: to entrust, and so to lend. Pecuniam alicui credere is to lend money, and that is where credit, creditor, creditworthy and credentials come from, alongside creed, credible, credulous and incredible. As a parenthesis in the middle of a sentence, credo means "I suppose" and is usually dry.