[rashidfar]

Hi dear Susan. Thank you for your illuminating answer. Applying the standards you have given the distinction between sub and co-ordinating relatives is clear. But using semantic standard, I meant to know whether the standards you mentioned comply with the semantic definition of Co and Subordinate sentences and what is the definition of them indeed? As you showed in previous answer, what I know at present about subordinate sentences is that they don't have independent meaning and we can't understand them unless they are completed by another sentence which is called main clause. So with this understanding I wonder whether the two clauses used in "while" sentence, for example, are main and sub clause or both of them are main clauses. For, if you separate them, each will have its own independent meaning.