[rashidfar]

Hi and thank you so much for your reply. Indeed, I think the best way to illuminate the students is to lead them towards the definition of sub and co-ordinating sentences which works all the time. which relative or connector does this function will be configured by themselves according to any sentence they are faced. of course, the categorization you mentioned at last is useful too. so, I think once more, the importance of semantical approach is obvious and it is a leading measure in most grammatical issues. and this phenomenon happens in many English words functioning in several ways. But what about "while and whereas" in the sentences I mentioned previously? are they coordinating in the sentences written? and, if so, why aren't they regarded as one of coordinating ones either?