I agree that the term "Imperfekt" really denotes a grammatical combination of past tense and imperfective aspect. That said, I always assumed (maybe wrongly) that the reason that the Imperfekt was so-called in German was because it used to mark an imperfect aspect, but that it has (mostly, or maybe completely) lost its ability to mark aspect and now performs a different role in modern German.
Does anyone know whether this is so? If not, what is the historical reason for using the term "Imperfekt".
You are right that aspect in German is now indicated by helping words (such as "gerade"). However, I was under the impression that the use of the imperfekt at the beginning of the sentence and then followed by the perfect would tend to suggest the right aspect more than they use of two perfects. So Ich schlief, als es passiert ist has a clearer aspect than Ich habe geschlafen, als es passiert ist. I beleive that Dirk was saying this. Please correct me if I am wrong. I never really did understand how to use the Imperfekt (I never use it at all when speaking German).
What is the best way to make this imperfect? Could you say
"Ich war am schlafen, als es passiert ist" ?
I stated that languages get simpler over time. I think this is true. If I recall correctly from my linguistic course (taken 20 years ago), there is even considered to be a law in linguistics. It is not, I believe, an exceptionless law, but exceptions are rare. Now, by "simple" something very specific is meant: the loss of structures such as inflection, tense, conjugation, etc. All ancient languages have far more of this stuff than modern languages. Also, most languages that are spoken in isolated places where there is little contact with outsiders preserve their complexity over the ages. I dare anyone to try to learn a language of Papua New Guinea.
Languages get simpler in the sense that the loss of the complex grammatical structures makes it easier for a non-natives to pick up the language. Languages are not difficult for native speakers.
The reason, I think, that linguists posit for the trend towards languages getting simpler is presicely because outsiders who need to use the language simplify the grammar. Its just too hard for them to learn the grammar. Witness Creoles and Pidgins. Examples of peoples who need to simplify the language include conquored peoples, who need to communicate with their new masters, and immigrants. Also, a situation where speakers of two dialects or different language come into contact with one another (no longer isolated), the language gets simpler.
I think that if a group of speakers remains isolated, the language change is very slow. Kids just speak exactly like their parents.