3rd person singular present only?

Question

The modal verbs will always take the 3rd person singular form of the present.

Is that always true? Is it not correct then to say something like:

¡Me acuerdo cuando se debía esperar afuera bajo la lluvia! (I remember when you used to have to wait outside in the rain!)

Gracias,

David

Silvia Piriz · Accepted Answer

Hola Dusty R.
When the lesson says that these impersonal structures take the 3rd-person singular, it means that the verb is not conjugated to agree with a subject. In other words, we do not say me debo, te debes, nos debemos, etc. It always stays impersonal.
However, that does not mean it must be only in the present tense. The tense can change (present, past, future), but the verb remains in 3rd-person singular.
Examples:
Presente:
Se debe esperar afuera. (“People must / one must wait outside.”)
Imperfecto:
Se debía esperar afuera. (“People used to have to wait outside.”)
Pretérito:
Se debió esperar afuera. (“People had to wait outside (on one specific occasion).”)
Futuro:
Se deberá esperar afuera. (“People will have to wait outside.”)
So your sentence is correct:
Me acuerdo cuando se debía esperar afuera bajo la lluvia.
Here you are simply putting the same impersonal structure into the imperfect tense, which matches a habitual or ongoing past situation.
Saludos
Silvia