sirgregory wrote:Example: I don't believe that he did it.
No creo que lo hizo.
no creo que lo hizo por su magnanimidad
I personally feel that there's a slight difference in the meaning. Unlike the phrase I don't believe that he did it.
, the phrase no creo que lo hizo por su magnanimidad
doesn't state that the author of the phrase doesn't believe (or doubts) that the unknown third party did it, they only questions the motive behind the action.
Interesting, from my language feel (Argentine Spanish), there would be no difference between the two in their meaning, and "haya hecho" sounds like the more natural version.
No creo que lo hizo por su magnanimidad = No creo que lo haya hecho por su magnanimidad.
In my opinion, the reason they are the same is because of context. The fact you are providing an explanation for the action (magnanimity), clarifies in this context that both interlocutors already agree the action did take place. Otherwise, it would not make sense to introduce motivation for an action. "No creo que lo haya hecho por su magnanimidad" would not make sense as a statement if the action's actual occurrence was still in doubt.
I do concede that using "hizo" does not sound unfamiliar here, so it clearly is out there in the vernacular. And as I mentioned, several sources clearly say the indicative form can be used to denote certainty, even in the negative, as you said. If I were questioning the motivation and not the actual event taking place, I would change the polarity of the main verb and say:
"Creo que no lo hizo por magnanimidad". (I think he didn't do it out of largesse.)
Or is the nuance different yet again? I mean, this is all nerd stuff here. In speech or even casual reading, no one stops to parse and split hairs over what mood was used in which tense under what polarity.