Coordinators are words that join grammatically equal units together. The principal coordinators are and, but, or, and nor.
Words whose function is to establish an unequal grammatical relationship, (e.g., that, for, to, whether, if).
(27) She asked me whether it was raining
Most subordinators can also function as other parts of speech: for and to can be prepositions, that can be a determiner, etc.), and so we will return to look at subordinators, and how to dintinguish them from other parts of speech, more closely in later chapters.