Number, Gender, and Case

From John D Cook comes this Grammar cheat sheet at Retinart. The opening warning reawakened in me a realization:

Please Note
I originally wrote this article for myself alone. It served as my way of learning the rules of language.
The fact that it got some attention mostly bothers me, to be honest, as I wasn’t intending for this to become some sort of authoritative source by any means. I worry this might be the case for a few, which I’m ashamed of as it was nothing more than practice and play for a literary child.
Reading through the comments makes two things clear: little, some, much, most of what is here is wrong. Secondly, what is right and what is wrong is subjective.
You would be much better off finding a much more substantial and educated opinion -– might I suggest The Elements of Style by Strunk & White? The Maira Kalman illustrated edition is quite lovely.

Many people have a confusion between grammar and style. Grammar is primarily concerned with matters of number, gender, and case. It is always wrong to use a singular noun with a plural verb. Or to fail to include a verb in a sentence. Failing to observe grammatical rules results in gibberish. Style is concerned with word choice, tone, length of sentences, and other such things. Ignoring style conventions results in text that is understandable, but may not be pleasing to the eye or ear. Or, it may actually sound better. Style conventions usually lag behind usage. Grammar admits of very little variation, while style is highly variable.

The confusion is probably fostered by a great many style guides referring to themselves as "grammars". Don't be fooled! And please, don't fall prey to the impression that your favored style is the only correct one. There are cases, such as journal submissions, where one must observe the specified style, but unless there is an external constraint, I find that euphony is the best style guide available.