What is the difference between “por si” and “por si acaso”?

Question

I learned that "just in case" should be translated por si acaso, but I have also heard por si used by itself without the acaso. I believe I've even heard si acaso without the por. What is the difference? Is it just stylistic, or are the cases where you must use one or the other?

Answer 1

In principle, the three combinations have different meanings:

• Por si acaso is an expression which adequately translates just in case.
• Por si might be a shortening of por si acaso. Perhaps you heard por si las moscas, and couldn't make sense of it. That is a slang variation of por si acaso. A couple of examples where it is used as a shortening of por si acaso are:

  Voy a hacer (algo) por si (algo).

  Cerraré la puerta con llave por si hay ladrones merodeando.

  Ahorré dinero por si llegaba la crisis económica.

However, I believe this is not a correct use of the language, though it might be common in some places. It doesn't sound right to me, at least.

• Similarly, si acaso sounds like a slang variation and not entirely correct (actually, it sounds worse than por si).

  Cerraré la puerta si acaso hay ladrones merodeando.

  Si acaso vienes a visitarme, cocinaré pavo para ti.