I find it difficult to know when to use “para”. For example, the expression
Nós fomos a Sintra visitar o palácio.
was recently used in a lesson, which translates to
We went to Sintra to visit the palace.
Another phrase I’ve come across in an earlier lesson is
Eles vieram para Portugal para viajar.
This translates to
They came to Portugal to travel.
So I have to wonder why “to travel” is “para viajar” whereas “to visit” is just “viajar” with no “para” preceding the verb. Would it be grammatically incorrect to include it?
Here’s another example:
Ela foi cedo para a praia.
She went to the beach early.
Nós fomos à praia.
We went to the beach.
Why is para used in the first case but not the second?
@pwsteele, with verbs of movement such as ir/vir, the preposition para is optional when you’re stating the purpose of the movement, and only mandatory (etiher para or a) when you’re stating the destination:
Nós fomos a Sintra (para) visitar o palácio
Eles vieram para Portugal (para) viajar
Between a or para, as in your last two examples, it’s largely up to the speaker’s preference, depending on how they perceive or want to express the duration of the movement (although sometimes, people use them apparently indiscriminately). Here’s a useful forum topic about that: “A” or “para” with verbs of motion? - Portuguese Questions / Grammar - Practice Portuguese
Basically, a usually suggests a shorter stay than para.