"Science" might not be the appropriate word but I think it conveys the gist of my question:
Is grammar always an agreed-upon, exact process among professionals when identifying usage and parts of speech (in the same way that you can rely on 2+2 to always equal 4), or can the lines become blurred when analyzing some of the more difficult aspects of it?
(For example, can there be a debate where a word's part of speech in a sentence can not be agreed upon, even though both sides have recognized and valid arguments?)
The reason I ask this is because I want to find better and more accurate ways of approaching and thinking about grammar. I am a beginner in grammar and I find myself thoroughly stumped attempting to analyze complicated and sometimes even simple everyday sentences. Most of the time, many of the words and usage of such words seem ambiguous.
I have always thought of grammar, and tried to approach it, as a black-and-white thing that can be solved with a formula. Is this correct? Is grammar black and white? Or do things get as muddy as they sometimes appear to me?