Why is English grammar so subjective?
I have a lot to say on this topic, but I’ll try to be brief. I assume what you mean by “subjective” is that people don’t follow the rules that you’ve read in grammar books. The problem is, these rules were mostly created in the 1700s, when the English language had already been around for a few hundred years. So people weren’t going to suddenly stop speaking English the way they did just because of some book. Also, there are many differences between the dialects of English, but some people think that differences are bad for some reason, so they try to pretend that they don’t exist, or claim that they shouldn’t exist. As a linguist, I believe (like all linguists) that langauge is highly systematized and patterned. If the language doesn’t fit a pattern we know about, chances are we just haven’t discovered the true pattern yet. In fact, discovering the patterns in language is what the science of linguistics is all about.