My sensei, who has been in this country for somewhere around thirty years, still has difficulties with this topic. It is as difficult for a foreign speaker as “wa” vs. “ga” is – and she had to ask us once which one was appropriate to use. So I thought this would be a good thing to post for Japanese speakers who are learning English. Here goes.
It is very simple for a native English speaker to know when to use “a” and “the”, and I honestly think it could be as simple for you too, if you remember one specific rule: the trick to choosing which one to use is based upon existence. Here’s what I mean.
If you are talking about something that doesn’t exist yet, then you use “a”. If it then exists, you use “the”.
For example, let’s use the example sensei was trying to use. She wanted to write on the board that we were going to participate in games, and she wanted to know whether “play a game” or “play the game” is correct. I told her it was “play a game”. This is because the game didn’t exist yet. “Let’s play a game” means that there are an infinite number of games, but since they haven’t actually taken form, we want to pick one of the games out of all of the possible games and play it, but we don’t know which one yet.
But once we start a game, we would then use “I need to go back to the game”, because the game exists, has taken form, and we then want to specify that that is the one specific game that we want to return to.
Note above that I said “all of the possible games”. This is perhaps more confusing, because I just said that we don’t know which game to play, so how could we use “the” to mark that there is existence? That’s simple – the set of all possible games is a single thing that has existence, so we want to use “the” to indicate that there is one thing that we want to speak of.
“The” set of all possible games, of which we will play “a” game. Oh, look. We’re playing a game now. Let’s start the game.
See how that works?
That third sentence became difficult, though. “We’re playing a game now”. Why is it not “the” game? Well, in this case, it actually could be. I prefer to use “a game” because while we’re talking about a specific game, the emphasis is not on the fact that we’re playing that game, but rather, on the fact that we’re playing any game at all. So even though we’re playing a specific game that has existence, we don’t really care about which game we’re playing, we just care that the activity we’re involved in is playing games. I imagine this is where you just have to get familiar with it enough to be able to choose the correct article. For me, “a” just feels right, but “the” feels okay. “That” could be used too, but only if you’re actually pointing at the game that’s about to start.
But for the vast majority of cases, just remember this simple rule and you’ll get it right 95% of the time.
Hope this helps.