How do I use "suponerse que +ind./subj." correctly?

Answer 1

As Thalia mentioned, the Indicative mood is for statements of certainty/fact, while one of the main reasons for the Subjunctive is doubt or uncertainty. One of the ways to determine if a sentence is expressing doubt is by the presence of the word no. No is often a trigger for the Subjunctive mood. (No creo que, no pienso que, no me supongo que, etc.)

 

I think these examples would be accurate - any native Spanish speakers, please correct me if I'm wrong!

1. Indicative: Se supone que los estudiantes ya están en el aula. (The students are supposed to be in the classroom already.)

2. Subjunctive: No se supone que los estudiantes ya estén en el aula. (The students are not supposed to be in the classroom yet.)

 

Hope that helps!

Answer 2

Use the subjunctive with form of suponerse que when there's some doubt involved.  Use the indicative when there is certainty. 

Answer 3

an example is "es de suponerse que usted fue primero" for " I assume you went first"

other example "es de suponerse que todos usaban cascos" for "I assume everybody was using hard hats" or "it obvious everybody was using hard hats"