Re: preverbs

     Okay,  I'll admit right up front that my Greek is all NT and learned from
sources like Machen, Dana and Mantey, BDF and some Robetrson.  SO I guess I
may be behind the times.  Can someone please explain to me or better yet, refer
me to an up-to-date grammer, which explains 
1.  What a preverb is? )Berbard Coulie)
2.  What a convertible proposition is? (Rod Decker)
Has our understanding 9f Greek grammar changed that much since these works 
were published?  I realize there is some disucssion over how many cases
there are and over the significance of time in tenses (the upshot of both
being that I'm left unsure how to doescribe what each tense is for, since
they all seem so fluid -- if they don't point to time, does any of them truly 
have a distinctive meaning?).  LIke I said, this is something I admit to being
"behind" on I guess, so please no flames.

Ken Litwak