Translation:Do you write letters?
I think the better answer that I'm beginning to see is that はdoes not mark the subject. Instead it marks the topic of the sentence. It would be the equivalent of 'about blank'. So "About movies, do you watch (them) ?" is 「映画 (えいが) は 見ます か。」So therefore a more smooth sentence in English "Do you write letters?" is 「手紙 は 書きます か。」 The object marking particle を isn't used because the object is inferred and therefore left out. After all, it looks quite redundant to write 「手紙 は 手紙 を 書きます か。 」 " About letters, do you write letters?"
-post is long, but I hope it helps.
(edit) - 手紙 is てがみ or letter in kanji. Thanks @mariodez and @anonamoose52. - (/edit)
I think you might be a little fuzzy on the use of particles は、が、 and を. But your sentence is almost correct. From what I understand of Japanese, your sentence should flow as "あなた(は/が)てがみをかきます. If you wanted to make 'letter' the topic and still use 'you' as the subject of the sentence (though it would be a little redundant), then I think the sentence would be divided differently. てがみは… あなた が かきますか？Something like that.
Japanese doesn't actually distinguish plural from singular very much. There are words for plural like 'these' and 'those' but they aren't used very often. And unlike in English where plural forms are conjugated (typically by adding 's'), I'm told that Japanese doesn't conjugate plural forms of words. So the translation is very context dependent on whether there are letters or just one letter. Therefore the question can be loosely translated either way.
I think what Julian ment is that because letter(s) are the topic, it uses a different particle then を(the particle for objects). Instead it uses the は (topic marking particle) to show that the conversation topic has changed to letters.
は (the topic marking particle) can override を (the object particle), but only if は was being used to intentionally change or bring up the topic of letters. There are other uses of the は.
Look at this site for a comprehensive understanding of は and が. (The more you know...) http://nihonshock.com/2010/02/particles-the-difference-between-wa-and-ga/
Not sure.... I suspect that there is a different phrase to make a suggestion. If you had changed your question to say "Shall we write a letter?" then I would point out the correct translation for that would be 手紙は書きませんか？As it is however, I don't know what the answer to your question is. I'd like to see an answer myself.
I would say the Japanese sentence for your sentence would be along the lines of "(わたしは)手紙を書きましょうか", but it would change depending on context/why I am saying it.
The verb 書くin its base form without any conjugations means "to write". So the sentence here with just parts would read "(implied noun) about letters write?" (or in the common tongue, "does (noun) write letters?). When the word "shall" comes in, it adds meaning that was not there in the question, the change being reflected as "SHOULD (noun) write letters". The sentence then isn't asking about if X simply writes letters, but if it's a good idea whether or not X writes letters...
A bit confusing and long winded, but I hope it helped. There probably are other, better reasons out there と思う.
I think I understand. So, "I am writing a letter" would be "tegami o kaite masu" but "I write letters" would be "tegami o kaki masu." One is describing an action you're doing now, and one is describing something you do normally, but are not necessarily doing right now. Do I have that right?
Yes, but bear in mind that "tegami o kaite masu" is a common contraction of "tegami o kaite imasu." The "i-" can also be dropped in "tegami o kaite rasshaimasu" ("You, sir, are writing a letter." If you used "orimasu" instead of "imasu," you could kick out the "-e" and say "tegami o kaitorimasu." (And, btw, "kakimasu" is one word, without the space.)