"a", "de", and "para"
How do you know when to use "a", "de", "para", or nothing at all before an infinitive verb?
Before infinitive verbs, you can try this (not a strict rule, but a good start, please notice that there is a biiiig range of possibilities, here are a few)
A + infinitive: turns it into some kind of gerund action.
Estou a andar = I'm walking
De + infinitive: it can be the cause of something, generally you can use "of/from" to replace it. And it's used to tell the usage of somethings:
Estou cansado de andar = I'm tired from walking
Essa barriga grande é de comer demais = this big belly comes from eating too much
Essa fruta é de comer? = Can this fruit be eaten? (is it real or plastic?)
Para + infinitive: indicates an objective or goal:
É para comer = It's to be eaten (I made these breads for you to eat)
Vim aqui para falar = I came here to speak.
Hint: Ask "what for?" (para que?)
Hint 2: You can see it as "in order to".
No preposition : normally a direct object just being itself.
Quero andar = I want to walk (WHAT do I want? I want to walk)
Please BE AWARE that MANY times, the other verb or the thing coming before the infinitive verb will define the preposition:
Gosto de andar = I like walking (this preposition is demanded by the verb "gostar", so it has nothing to do with the given explanation about "de")
Ele começou a falar = He started to speak (Like "started to" in English. You always use "start to" or "start gerund", but gerund cannot be used that way in Portuguese)
Just a note: The gerund differs from Brazil to Portugal So "Estou a andar" would be the expected in Portugal, but in Brazil would be weird. Here we use "Eu estou andando".
That last sentence pretty much sums up everything about language learning. I'll give you half a lingot for the good explanation and another half for that :)
What is the function of “a” (before fazer) in this sentence please?
O melhor que você tem a fazer é aceitar
I’m guessing it’s that “tem” takes a noun-like object, so requires “a fazer” as it’s a gerund.
So literally, something like: “The best that you have ‘for doing’, is to accept.
Am I close?!
I noticed a structure that seems to be followed in this sentence (and others) which is ter + algo + a + infinitive but, as to the reasoning behind it - "Eu não sei"! I think the sentence may translate as The best you (can do)/(have to do) is to accept
Unfortunately prepositions vary from language to language so it's pretty hard to give any clues. Over time you'll learn which preposition fits better in certain cases and what prepositions are supposed to be used along with the verbs...
Para + verb can also indicate "in order to". Not a big difference from "to" but a lot of the time that extra meaning gets dropped