When subjects are the same - subjunctive errors?

Question

I see in this lesson that when the subject is the same, we should be using the infinitive. I need to work on that!

Is it ever a “tolerable” error among native speakers to commit this mistake when using a colloquial register? I frequently want to say things like “Dudo que (yo) pueda hacerlo para viernes” instead of “poder hacerlo.” I know you’re here to teach us the right way!! Just curious as to “how” wrong it is.

Accepted Answer

Hola A,
yes, let's say there is some flexibility when using the infinitive or the subjunctive with the same subject in both clauses. You will definitely hear sentences in a more relaxed /colloquial Spanish like:
Dudo que llegue a tiempo. (same subject: yo)
Duda mucho que pueda asistir a la reunión. (same subject: el-ella)
instead of:
Dudo [poder] llegar a tiempo. 
Duda mucho poder asistir a la reunión. 
Saludos