This thread is veering away from Dorio's thread. I think the discussion is interesting but I'm wondering if a new thread could be started about grammar. As it is informative but will certainly be missed by someone looking at the title "Using curse words".
As a amateur linguist, I've studied many "grammars", so my perspective when I read the thread is that there are three different interpretations being given to the word "grammar".
1. 'Grammar' is the organization (syntax) and modifications of words (inflections, etc.) to provide meaningful (semantic) sentence in a language.
-- This is the part of the thread where many people chime in. To be understood by an English speaker, it needs to follow the innate structure of English. Even people who are illiterate can grasp and learn to speak "proper" English. This aspect of grammar does not require it to be committed to writing. The reference to 'Yoda-Spanglish' kind of suggests that the utterance (written or spoken) needs to sound like the intended language. English is Subject-Verb-Object (SVO). Other languages have different orders: VSO, OSV, SOV, and more exotic. From the standpoint of this definition, "grammar" is learned without study but there are ways of writing or speaking that are "ungrammatical". This 'definition' however does allow for language change. There are 'learnable rules' that make utterances 'meaningful'.
2. 'Grammar' is a codification of the rules for proper writing and speaking among language speakers.
-- This part of the thread seems to raise the majority of the dissent. For academic purposes, 'grammarians' have developed a unique jargon, sometimes arcane, to dissect and analyze speech and writing. This, however, is true of every language that starts navel gazing. Sanskrit, Greek, Latin grammarians over a thousand years ago started the practice. Whether you have "passe simple/composee", "piel/pual", "animate infixes", "aorist tenses", "reflexive constructions", etc., these 'grammarians' dissect their languages. Now that is good because we do benefit from thinking about what and how we speak because it is the basis for how we think and organize thoughts. And it makes it teachable.
Do I think that a person must be fluent in the jargon such that "iambic pentameter", "ellipsis", etc.? Not necessarily. One needs a basic grasp of grammar rules helps to construct sentences. When I learn a language, I want to be understood so I need to master some basic rules. "I of name as-for John is" is poor English but is good Japanese "Watashi no namae wa John desu." It helps to know about "coordinating particles" like "wa", "o", "de", etc. Does it mean I get them right? No. That comes with practice and exposure. Learning any language, one learns the "formal" language. The Japanese taught to beginners uses "polite" forms rather than "abrupt" forms. The real challenge is understanding a film, television show, or song in another language when "formal" is out the window, if ya' gets what I'm sayin'.
3. 'Grammar' is an internalized template for generating utterances understood within a language community.
-- This is by far the most abstract of the definitions. For transformational linguists, grammar is dynamic. It is widely held that humans are "wired" for speech. All children seem to move through a sequence of skills in learning a language that then hones in to a specific language--sounds then nouns then adjectives then verbs. "B"--BALL--RED BALL--BALL FALL--RED BALL FALL DOWN--...--The red ball fell off the couch.
So tying in definitions (1) and (3), we all "learn" our language not necessarily by writing. Xhosa, a click language, has rules that are learned by five year olds yet were unwritten until relatively recent times. In studying heiroglyphic inscriptions, Egyptologists have found "grammar errors" by scribes. These are only known from having studied thousands of inscriptions and developing a "grammar jargon". The "st'm-f construction" has meaning only among those who've studied the language. It clearly wasn't mentioned by the Egyptians as it was implicit, though non-native scribes seemed to mess it up on occasion. And when I've read manuscripts by native Spanish speakers, I find grammar and spelling errors ("Que ases? La policia bienen. Corre!" => "Que haces? La(s) policia(s) viene(n). Corre!"). It's not just English writers who make 'grammatical and spelling mistakes'.
The issue is being readily understood. That's where (#2) comes in. I'm not suggesting we have the English language police. Some errors are easier to look past than others. "Their are" for "there are" can be a simple typo. When the errors become so distracting that you can't understand the meaning of the text, it's a problem. Rather than see the masterpiece, what is present are grey globs.
Yes, if a word is circled then I can know it's wrong, but it doesn't always tell me why, what it should be or if to include it at all. The use of "zhe" in Russian is very idiomatic like "ja" in German. I can research it and learn over time. Punctuation in other languagues can follow different rules from English. If nothing else, English writers should learn to use the comma--sparingly.
There is an excellent poem by Charles Battell Loomis called "O-U-G-H" that captures the frustration of trying to apply what one thinks one has learned to the wily beast of English spelling. And THAT would be lecture in itself.
The spoken elements of the language are innate for native speakers (#3) and some forms must be learned (#1) like lay/lie and set/sit. 'Lay' and 'set' are active, something you do to an object ('transitive'). 'Lie' and 'sit' are actions which something does ('intransitive'). Misuse of those is what I most often see.
Now, "Does a screenwriter need to know 'grammar' to write?" can be interpreted a variety of ways, which seems to be what's happening. For the purposes of getting a script past a reader, the writer should have a firm grasp of basic terms and written rules as in (#2). The writer doesn't need to know esoteric terms like suggested in an earlier post. They just need to know how to make subjects and verbs agree, know the difference between adjectives and adverbs, have some reasonable understanding of verb forms and a basic notion of using relative pronouns (who, what, which, whose, where). It helps to review using commas. Other than those basics, most writers have an innate sense to construct English sentences.
We pick up dialects from listening. If you watch TV, you can distinguish regionalisms--Southern, New England, Midwestern, British, Hispanic, etc. We can listen and learn without writing. "If one listens to the Queen's English, some of the elocution and elaboration will be learned indubitably." And I believe that practice writing and speaking will make you better at creating sentences (grammar, in all senses).
Grammar is not about creativity. It's about expressing one's ideas. And if the writer can't do that, well, it's like the solitary tree falling in the forest. And over time, the inability to garnish recognition can crush creativity and motivation. It shouldn't stop a writer from committing ideas to paper. But the writer wants to have it read, s/he needs to have a goal of improving in his craft which means learning to follow the rules of the language in which s/he writes. If one doesn't strive to improve, skills degrade. If one wants to be successful, one needs to push one's self to develop. In this industry, mediocrity and status quo don't cut it.
In writing for a current project, I need to follow the 'grammar rules' for Klingon. Needless to say, there are those audience members whose Klingon grammar is stronger than my own so I keep Okrand by my side. If grammar is important to the audience for an artificial language, it's no less so for English for the script reader. Beside me when I write are my thesaurus, a collegiate dictionary, and a English grammar text. Fortunately, my laptop and software provide all three. I just need the good sense to recognize when its suggestions are wrong! And in this age, there is NO EXCUSE for not using a spellchecker on one's manuscript. Anyway, good writing!