Omitting particles like wa and ga

Hiya!

Through exchanging mails with my language partner I have noticed that particles are sometimes skipped.

As an example; ''日本語とてもお上手ですね！''is what was written. But isn't it supposed to be ''日本語がとてもお上手ですね！''?

Apparently, I don't deserve the praise, seeing that I don't quite understand the reason ''が'' was omitted.

What is the norm?
Why wasn't ''が'' used?
Anyone have any insight on the matter?

Thanks beforehand and cheers!

- Yes, that's what's supposed to be, with "ga."

- In spoken language, AND in colloquially written friendly e-mails/letters, such omission can happen very easily.

Particles of all sorts get dropped during more casual speech and writing. This is mainly because it saves time (the implied particle is usually fairly obvious, and even if it's not, you still understand the meaning of the sentence, so saying it becomes unnecessary. This is a lot like dropping subjects [aka 私 and people's names] once they've already been made clear), but sometimes it happens when someone is confused about which particle to use. If you had trouble remembering that "ride the train" is「電車に乗る」and not「電車を乗る」but knew that dropping the 'mystery' particle wouldn't destroy the meaning, you'd probably get accustomed to saying「電車乗る」all the time.

That being said, dropping particles doesn't always work out and dropping all of them is never a good idea.

For example,「パーティに行く」can be said like「パーティ行く」and still make sense. There's a party and you're going to it. However,「田中くんのパーティに行く」can't really be changed to「田中くんパーティ行く」and still make sense. The second one sounds more like a request/demand/question aimed towards Tanaka, or like you're explaining to someone where he's going.

The general "rule" would probably be that you can drop は, が, を, and に and still make sense, but で and の should be left as is. If you'd like to try using this, just think to yourself, Would I understand this phrase without that particle? and drop it if the answer is yes. It'll start coming naturally after a while.

Also note that dropping particles is less casual than using them. If a sentence requires です/〜ます, you should probably keep the particles. Dropping は and が is done frequently enough that a lot of people may not notice or care, but it's good to stay in the habit of using them when you're trying to be polite either way.