The accidental se: se me cayó

The accidental se at a glance

Three pieces always come in the same order: se, a pronoun for the unlucky person, then the verb. The thing that fell, broke or got lost is the subject:

The pronouns are the indirect object set from object pronouns. This se is not the reflexive one of reflexive verbs: nobody does anything to themselves here.

The verb agrees with the thing

The thing is the subject, so the verb matches it: one thing, a singular verb; two or more, a plural verb. The person changes nothing:

An infinitive or a whole clause counts as one thing, so the verb stays singular:

• Se me olvidó llamarte. - I forgot to call you.
• Se me olvidó que hoy no había clase. - I forgot there was no class today.

Whose fault? Three ways to say it

The same broken glass can be told three ways, and the grammar decides how much of it is yours:

Rompí el vaso is correct, but it says you did it and takes the blame. For a genuine accident, Spanish reaches for the middle one. Forgetting works the same way, and all three of these are correct:

• Olvidé las llaves. - I forgot the keys. (plain olvidar)
• Me olvidé de las llaves. - I forgot the keys. (olvidarse de)
• Se me olvidaron las llaves. - I forgot the keys. (it slipped my mind)