Why isn't there preterite (pretérito indefinido) in the subjunctive mood?
Also, what do I use instead?
modified the answer a bit, so hope it makes sense now, but the imperfect does not refer to direct discrete completed actions, which the preterit does.
In relation to your comment below, all i can say is 2 things, 1. by adding I'm happy that meansing the following clause is now a subordinate and basically acts as a description for the main clause. 2. if you want to look at it that way, great, but just remember there is no´preterit subjunctive form in spanish, so i guess good luck
Fine...take any preterite sentence you can think of and add "I'm happy that" before it.
For example : "I'm happy that you ate dinner with me this evening."
It's complete and it happened one time in a specific time frame.
In this case, Spanish could use preterite subjunctive.