Grammar rules began because people speaking the same language needed a universal way to communicate what they meant in sounds to someone only looking at words or symbols (rather than hearing the words spoken). Originally, people used individual symbols to stand for different words or ideas. Eventually, people began using symbols to represent specific sounds. At first, the only symbols used were for the letters of the alphabet. In fact, oftentimes words were not even separated by any spacing (c.f., original handwritten copies of the New Testament were written in all capital letters with no spacing between words). Then as writing developed (especially after printing made books more available), symbols were created to indicate inflection (tone of voice--period for a statement, question mark for a question), pauses (commas, dashes), and other characteristics of spoken language. As time passed, people began to try to standardize the rules governing spelling, grammar, and punctuation so that everyone would be able to agree to the meaning of what was meant in a piece of writing. Since most of these rules developed out of everyday speech (the sounds of words), they don't always appear to follow any logic.
Oftentimes when students have problems with grammar, it is because they are putting into print what they are hearing when talking rather than using the standard rules that were developed for writing. For instance, a student might write, "I'm gonna go to the store," using gonna for going to. Once I had a Latin-American student who thought shoulda was a word because he had heard people say it. The students in my class quickly explained that the correct spelling was should of. I had to tell them that this wasn't correct either. What is actually meant is should have, but it is easy to see how someone could mistake the sound of should've (contraction of should have) for should of since they sound the same. Writers have to work hard to break any bad habits they may have developed in recording sounds when writing.
ENGL1010 Composition I