[susan53]

Rashid said : but can't we have a definition of what a subordinating clause is? That's easy - it's one which can't stand on its own. It may be introduced by a conjunction - eg because, by a wh- word (eg relative pronouns), inversion or by a non- finite verb - etc etc, but in any case it makes no sense without an attached main clause. Some examples ...

Seeing the number 10
because he was late
Had I known

These only make sense if you add another, main clause :

Seeing the number 10, he suddenly remembered the appointment
He skipped breakfast, because he was late
Had I known, I wouldn't have come.

As for the distinction between co-ordinating and subordinating conjunctions, well that's defined in my previous message. The problem is that it's not absolute. there are some words (like "for") which "sometimes seem to act as co-ordinators and sometimes like subordinators. Quirk et al (Grammar of Contemporary English, Longman) describe it as a gradient, with the "pure" co-ordinators at one end and the "pure" subordinatiors at the other, but with various items in the middle - acting sometimes like co-ordinators and sometimes like subordinators. So sorry, Rashid, but no - there is no clear cut distinction.