Grammar questions from Marcelino Pan y Vino by José María Sánchez-Silva

[aleCcowaN]

In "por si la veía", "por" looks more like a "nexo causal" than an adverb. I cannot say the whole phrase is an adverbial clause, but I wouldn't be surprised some stretch of grammar rules could see it that way, just not to leave things unexplained. I wish I hadn't cut or snooze through so many Castilian classes in High school.

[Quaeso]

Thank you, so is "por si..." the same as "por si acaso..."? And do they take an indicative verb always?

[poli]

Not always. If there is lots of doubt, you can use the subjunctive.

[aleCcowaN]

Thank you, so is "por si..." the same as "por si acaso..."? And do they take an indicative verb always?

In the context of the text, both por si and por si acaso are conjunctional phrases meaning "in case" or "just in case", they anticipate a possibility and take mostly indicative.

But por si acaso can also be an adverbial phrase by itself meaning also "just un case" but introducing a precautionary measure, taking mostly subjunctive

Por si acaso llueva, lleva un paraguas.

But acaso itself can mean quizás, so there are too many things varying ay the same time so no general rule should be expected.

Without knowing neither the storyline nor the context of the phrase "por si la veía" tells me about a kid who thinks that looking at the sky (=heaven, both in Spanish, Biblical Hebrew -shamayim- and Koine Greek -ouranos, or ouranoi, to match the style of Hebrew ) they can "columbrar" (guess-glimpse) their mother's soul. It takes indicative because in the kid's mind that's a reality looking for a chance to occur and not some speculative notion sustained by wishful thinking. The mood chosen gives me this conviction.