A recent thread, asking about use of the comma in conjunction with ‘and’, had many replies stating that the exact use is dependent upon which stylebook you are using.
How exactly does style differ from grammar? Where does one end and the other begin?
Rex Stout, who wrote the excellent Nero Wolfe books, discusses this point in his autobiography.
One point he makes is where authors choose to break for a new paragraph. That’s clearly style (and he’s right - it does make a difference!)
Grammar is the rules of the language, including such things as subject-verb agreement, transitive/intransitive verbs, whether an adjective goes before or after the noun, how to conjugate a verb, what verbs are irregular, etc. It is both written and oral.
Style is primarily oral. In a language sense, it involves such things as how to capitalize, how to indicate a book title, serial commas, what compounds to hyphenate, standard abbreviations, footnote formatting, etc. A good example of a style guide is the USGPO Style Manual; browse it to see what it covers.
There is a relationship between the two, but grammar is standard throughout the language (You wouldn’t say, *He wents to work), while style is, ideally, consistent for all documents from the same source, but can be different with documents from another source. For instance, Playbill lists play titles in italics and movie and TV titles in quotes; other magazines italicize all; newspapers quote all. All are correct for the publication involved, since they are consistent.
Grammar is what you HAVE to do.
Style is what you WANT to do.
Grammar is the underlying structure or framework; style is the bells and whistles (or lack thereof, if you’re a Hemingway wannabe).
Grammar is as mentioned a set of rules that for the most part are consistently interepreted although there is some room for gray areas while style on the other hand addresses the look and feel of a piece of writing and includes such matters as how well a piece communicates the intended meaning and for example the acceptability of writing extremely long sentences without punctuation such as this one which is grammatically correct but stylistically a complete and utter disaster.
Manatee has hit the nail on the head
You’re missing a period, and no style guide will save you now! 
You meant to say that style is primarily written, didn’t you? If so, I agree with your post completely.
There are also distinct academic styles: MLA is the most prevalent, but some schools/publications use the Chicago Manual, while psychology, I think, uses another style altogther. The differences are minute (between MLA and Chicago, anyway), but some professors can be anal about which style they prefer.
A grammar question and its answer belongs in GQ; a style question and its answer belongs in IMHO! 
Except- in English, there is nothing you HAVE to do. There is no rule-making body. In English, the only two “rules” are: have it be understood, and follow a common usage. There are no other “rules” of grammar. Once the wording is easily understandable and fits within A common usage, it’s “follows the rules”.
Now, true- some employers have a “style manual”- such as the Chicago Manual of Style and insist you follow that. In that case, as long as they are writing your paycheck, you follow the usage they prefer.
English has grammatical rules. For example, the adjective usually goes before the noun it is modifying. e.g. “The cat black walked.” is ungrammatical.
Or from Wkipedia
“English is an intonation language. This means that the pitch of the voice is used syntactically, for example, to convey surprise and irony, or to change a statement into a question.”
I think what you mean to say is a good point, though, which is that the grammatical rules of a language are determined by actual usage, not by style-books or government agencies.
I think your last sentence here contradicts your first.
You HAVE to be understandable and fit within a common usage. You don’t need a rule-making body to enforce that (and fortunately the English were never able to emulate the French in that regard).
Or, in other words, what J a j said.
I would say that one way to define the difference is that when a particular choice results in confusion or loss of meaning, it crosses the line between style and grammar (taken broadly, since strictly speaking, punctuation is not a function of grammar). Of course this is a very fuzzy line, since one man’s confusion is another’s artistic epiphany, and in some works, “errors” in grammar, syntax, or punctuation may be stylistic choices. (I would have hated to be the copyreader for Joyce’s Finnegan’s Wake.)
But in periodicals or other works in which multiple writers are contributing to a whole that is intended to be consistent, the stylebook establishes which optional usages are standard.
As an example of where style choices can cross over to “errors,” people arguing in favor of the serial comma often present the following example:
“I’d like to thank my parents, Madonna and God.”
The absence of the serial comma following “Madonna” creates a (presumably) unintended implication. (Furthermore, those who oppose the serial comma can offer no significant advantage to not using it, except for the infinitesimal saving of space.)
Except where such arguments can be made, styles are choices that cannot be labeled as objectively incorrect, whereas grammatical errors can be.
While it is true that there is no Academy imposing rules on English speakers, there are any number of rules in English.
If there were no rules, you could have said, “There am no rule-making body.” Someone might argue that since the meaning is still discernible, it’s not an error. Certainly, there are no Grammar Police to punish such constructions. And if that sentence appeared in a work of fiction or a poem, the usage might be accepted.
But in standard English, non-fiction writing for a general audience, that sentence is wrong because it breaks the rules of grammar. The real rules of grammar. Rules that we don’t always recognize as rules because we follow them without thinking. But rules nonetheless.
[Note that I have tactfully overlooked your numerous errors in punctuation. ]
Like I said- there are no rules of grammar other than: having it be an established usage, and be readily understandable. In the case of “There am no rule-making body.” it could be argued, as you said, to be understandable, but it’s not a standard usage.
For example, the “serial comma”; once we have placed- or not placed- a comma to ensure proper understanding, either usage is standard, thus either usage is correct. True, the Chicago Manual of Style says one usage is right and the other isn’t, but other Manuals of style disagree.
Therby there are no “rules”. There are “usages”, and a need for the wording to be understandable. If one wishes to end a sentence with a preposition (a big “hobgoblin” to some Grammar Police), then despite what a “manual of style” may or may not “rule”- it’s OK to do so, as long as the meaning is clear.
Oxford, for example- lists usages. They don’t try to “rule” whether one usage is “right” and another is “wrong” they simply cover such usages as are standard. It’s called “descriptive” or “descriptivism”. Making "rules’ is “prescriptivism”.
In France, they have an actual Body of National law on what words, grammar and such like are “legal”. :rolleyes: That’s the ultimate example of “prescriptivism”. We have nothing like that in the USA (thank gawd) and in fact, there are usually several disagreements between such “style manuals”. In fact, there’s nothing to stop dudes from coming out with rather strange “Manuals”- which has happened, like with some simplified spelling ideas. (some of which were great, and others- not so much.)
Descriptivism is in. Presciptivism is out. Sorry.
Trying to be Presciptive with the English language is like Canute and the Tides.
Quebec goes one better and adds in the Language Police. Admittedly, their work is mostly related to controlling the use of English, but they also rule on the standardizing of official French language rules and vocabulary.
Th’art soothly spoke, O misspelt death-wight, whilst thou saist that the English, she hath no prescriptivism. But when thou hiest thence to the proposition that there be no rules, thou couldst not be farther erring. There being usages the which comprise consensus custom as to how the language, she is spake, the christening thereof as “rules,” the which describe usage, is not wrongly uttered.
Or, in simpler terms, English has “rules” that describe how various subcultures within the English speaking world use the language in various contexts, ranging from formal scientific or scholarly papers to the conversation of teens whose 'rents may be listening. Just as it’s completely improper in both formal and colloquial Spanish to use the passive (except in very strained contexts) to identify what an inanimate object is termed, but instead, by an idiomatic construction, the reflexive is used, producing sentences that translate to “This mineral calls itself hornblende.” A childless Russian will not say “I have no children” but “By me there is nothing of child.” The literal translations of the normal English sentences “This rock is called hornblende” and “I have no children” are wrong – not because the Imperial Spanish and Russian People’s Language Authorities declared them so, but because they do not correctly apply the proper grammatical and syntactic structures of Spanish and Russian. And “You am wrong to saying English have no rules” is a similarly grammatically incorrect sentence – though true in its meaning, because it itself violates the consensus “rules” that English speakers normally use.
DrDeth: Okay, if you want to define “rule” as “a pronouncement by an established authority on what is and is not correct,” then I agree, there are no rules in English. From your post, it looks like you used the term “usage” to describe what I would call “rules.” So our disagreement is just a question of semantics, but I think your definition of “rule” in that sense is needlessly restrictive, and not a common usage.
The fact is that all languages, even those that have a language police, are constantly changing, and I never said otherwise. However, most of these changes are necessarily small and slow. The vast majority of what you called usages, and what I would call rules, remain unchanged over relatively long periods of time. That stability justifies the permanence implied by the word “rule.”
True, if large numbers of people started saying “There am no rule-making body,” that rule would ultimately change. And many people might complain along the way that “am” is wrong. But it might eventually become the new rule. That wouldn’t make it any less a rule.
(On preview, nicely put, Polycarp.)
Yes, I consider “usages”= “guidelines” as opposed to the stricter term “rules”. Thus, there are- by that definition- no rules, but there are guidelines. The “rules” or “guidelines” of the English language are more like the “rules” for a childrens playground game, as opposed to the “rules” of Major League Baseball. 
Good post, though. 
And Poly- hilarious!