Thank you for your excellent response Martin. Yes I agree with you that this is target language best left for high intermediate to advanced learners.

Unfortunately, though, it was introduced in a text book for first year intermediate learners at this university. I do have the creative license to use this text book foundationally; however, my students exposure to it created enough curiosity on their part that it had to be addressed. And, as you can well imagine, the textbook treatment was woefully inadequate.

Furthermore, I also agree that the past simple needs to be brought into the discussion fortunately I did that as well and it seemed to help a little.

Your advice that I think will be the most useful, and Ill definitely apply it, is that of the controlled practice / reinforcement exercise with alternatives. And the graph concept looks to be a good one also.

Over-use and under-use, as you discussed it, is a very valid point also. I would do this and I would do that can be very redundant. I sort of had that feeling while last addressing the issue, but I was reluctant to steer them away from the task at hand.

And finally, I agree that it is unlikely that such language will quickly enter into the realm of their communicative competence but can serve a purpose in terms of creative thinking or consciousness raising. Enabling students to see the beauty of the language itself, expressed as it is by such intricacies coupled with a refined simplicity, is half the battle isnt it? When they have attained an actual appreciation for the English language its ability to flow and yet maintain precision, their learning becomes more meaningful, doesnt it?

Thanks again for your time and trouble Martin.