Is "por" used much more commonly? Are there any estimates of percent (e.g. por is used 70% of the time while para is used 30% of the time)
The current absolute frequency of por in Spanish texts is around 0.81%, and 0.57 for para, the former is used 59% of the time while the latter is used 41% of the time.
According to this page,
por is used more than
Por is the 12th most used word in the Spanish language.
Para is the 15th.
This makes sense because
por is only a preposition, while
para serves many more purposes. If something only serves one purpose, it's going to be used a lot, like definite and indefinite articles; you're never going to see them used as anything else, and that's why the number one used word in Spanish is
el/la, just as in English, the most common word is
These two prepositions when interchangeable in some cases, in most of them they are not. As a rule of thumb, let me prove it with these explanatory examples:
(Yo) lo hago por ti (in your honor) [non-physical complement]
- Estoy rezando por ti (You can't say "estoy rezando para ti")
(Yo) lo hago para ti (I'm doing this to give it to you) [physical complement]
- Estoy escribiendo un poema para ti (You can't say "Estoy escribiendo in poema por ti")
However, there are cases where "por" and "para" are interchangeable like in:
- Estoy estudiando por/para algo. You can find this phrase with both prepositions. Cause "por algo" (for something) is frequently used to specify that something isn't random, to specify that something is made for some reason.
P.S. So the question should be when do we use "por" and when we use "para" and in which exceptions we can use both. Cause otherwise you are asking for the relative frequency of two preps that are in most cases used for different things. I hope I made it clear to you, cause this, in particular, is not an easy topic.