The grammar of our language is not a body of divinely inspired rules. We are dealing when we venture into the confines of English Grammar, with no set of immutable rules ,with no absolute distinctions. Grammar is not Mathematics .In Arithmetic 1 and1 is two, in Geometry , the sum of the squares of the arms of a right triangle equals the square of the hypotenuse . In Algebra (a-b)(a+b) equals (a2-b2).
These are all facts which no one in his right mind would care to argue. They have been demonstrated to be true and are accepted the wide world over. There is simply no ignoring and changing them.
Grammar is not like the natural sciences. In Physics, a body falls down – no human power has any influence on the law of gravity; in Chemistry , water freezes at 32’ Fahrenheit and boils at 212’ Fahrenheit whether we like it or not; and in Biology, the one-celled amoeba reproduced by a process called Binary Fission.
These are all incontrovertible facts; they were true thousands of years before man discovered them and they will continue to be true as long as earth turns. Exact sciences like Mathematics, Physics, Chemistry and Biology are thus seem to be comparatively dull and static, unlike Grammar in which there is constant change.
Grammar deals with one of the higher activities of human beings (the translation of thoughts into words) and is as dynamic, as unreliable, and as unpredictable as human beings themselves.
When you deal with a study (like Grammar or History or Semantics or Psychology) which is deeply involved with the human equation you will be wise to expect no exact laws, you will do best if you look askance.
English Grammar, as a science, attempts to make an accurate record of what people say and write , or how they phrase their thinking into sentence patterns. Just as Chemistry, Physics and Biology study and record the phenomena of nature, so Grammar analyzes the phenomena of human communication.
The grammar of a living language takes note of any usages that have currency. Thus an expression is a part of English Grammar if it is used by a considerable number of people whose native language is English.
Common usage among educated speakers is the sole yardstick by which correctness in Grammar is judged. “Laws of Grammar” by themselves have no validity unless they are based on educated custom, usage, habit, convention. As convention in language changes (and it often does) , the “laws ” changes also. A rule of Grammar is valid so long as educated users of English generally abide by that rule.