"They write a letter."
Translation:Eles escrevem uma carta.
Yes, the subject pronoun is used more often in the third person because there is gender information. (ele, ela, eles, elas) = (he, she, they -all males or mixed-, they - all females).
Eu, nós, and tu, don't provide any gender information, so the subject pronouns in first (eu, nós) and second person (tu) are superfluous, whereas third-person subject pronouns are not superfluous.
Note that você and vocês are conjugated the same as third person
If you just say "Escrevem uma carta", you don't know if it's elas, eles or vocês.
Or if you say "Escreve uma carta", you don't know if it's ela, ele or você.
Non, I meant that I put "letra" and got it wrong. I was giving a definition for the intended use of "letra" as separate from the definition of a "letra" as a character in the alphabet for the sake of clarity. It didn't occur to me at the time that it was also a cognate. :)
Okay, "letra" should have been accepted! Thanks. :)
Even so, if "letra" only meant the letters in the alphabet it should have accepted it anyway. We can have all of the children write letter "A" or the letter of their choice.
The books I checked weren't conclusive, so, I found this. http://en.wiktionary.org/wiki/Appendix:Portuguese_pronouns
"The subject is always before a verb. Due to the high number of verb conjugations, this pronoun can be omitted if superfluous: Eu comi arroz ontem.; Comi arroz ontem. — “I ate rice yesterday.”"
It's exactly the same thing in French, except you can't skip the pronouns.
In Portuguese, as explained above by ThanKwee, it's not good to skip the 3rd person pronoun, because you don't know from the ending if it's a feminine or a masculine (see explanations given by ThanKwee)