We don't formally know the rules of English grammar, unless we are linguists. For example, if I had to explain the use of definite and indefinite articles in this stanza

The way a crow
Shook down on me
The dust of snow
From a hemlock tree...

to someone learning English, who didn't have articles at all in her native language, I couldn't do it without great effort, and I'd probably be wrong. Instead, what we usually do is say, "listen enough to how these articles are used until you get the hang of it." In other words, develop "native speaker intuitions" of your own. Even if I were a great explainer of grammar, the person I explain the rules to might not be capable of both 1) Understanding a set of abstract rules, and 2) Applying these rules consistently the way a native speaker would. If I substitute an "easier" rule, one that accounts for many but not all cases, the rule will be easier to understand and apply, but will likely lead to errors. In fact, the student is likely to simplify the rule on his own.

Frost could have written

The way the crow
Shook down on me
A dust of snow
From the hemlock tree...

but not "A way a crow..." I have no idea why. Just sounds wrong.

People who are not linguists, but who think they know grammar, are the worst, for they will tell you it's a grammatical mistake to say "smarter than her."