Most Grammar software slices and dices my dialog. Of course I know "Gonna and gotta" aren't exactly grammatically correct and I know I often slip between active and passive voice. I've rewritten paragraphs so that my software finds no problems but they sound "Stiff" if that is a good term. Is there some middle ground between what is "Correct" and what is right for my story?
Others on this site have far more expertise than me on this subject, but I have learned a few things. During a screen play writing seminar in Carmel [wonderful place!] the facilitator demonstrated some past movie disasters where the screen writer was also the original novelist. The dialog was horrendous--laughable. In real life, people talk in short, often incorrect bursts, and that is fine for a movie, but would be difficult to read for very long. Novels allow the characters to speak in unusually long stretches, and that reads fine. It is quite acceptable, but that exact same dialog in a s/p would be horrible. So, even though the written story allows for a great many latitudes, some lines you probably should not cross. I have some low life characters who speak "gangsta" because that is believable, but in the dialog exchange with say, a cop, and that is escalated to a slightly more correct level. Now when that same cop talks to an educated person in the DA's office, the speech is normally a bit more correct. This is not a very good answer to your question, but I would tend to overlook errors the s/w finds in dialog. However, the s/w is probably good for the narrative portions.
Don't write dialogue in proper English, unless the character has a good reason to be speaking in such a manner. For colloquialisms and informalities of speech, I use the "add" command to add the word to the word-processor's vocabulary. Your word processor should not dictate what goes into your story.
Word processor grammar checking, and for that matter, any grammar-correcting software, is notoriously unreliable. You can use it to point out where you should take a closer look. But if you find its suggestions distractions, just turn it off. The English language is too complex for a computer, until computers can actually understand the meaning of the writing, including keeping up with slang. Even then, you'll have to ignore sentence fragments and other grammar lapses-by-choice. If you don't feel certain about your grammar, learn it. If you do know your grammar, trust it (but be open to learning anyway). But don't become technology's willing slave.
Thanks for the fast response. When my "Electronic Editor" makes a suggestion, I pay attention---until I totally disregard the suggestion. I have a copy of Strunk and White's "Elements of Style" 1st edition on my desk at all times. My particular copy saw me through Freshman English in 1959-60 and has been a valued friend for the past 50 years. It is yellowed and dog eared but still usable. Notice the "---" in the second sentence above. What is the correct punctuation? I tend to do this a lot.
An em-dash is signified in manuscript by two--not three--hyphens. It should be neither preceded nor followed by a space. The exception would be when it is used to indicate an interrupted literal thought, which unlike spoken dialogue, would not be enclosed in quote marks.
Dialogue doesn't have to be grammatically correct or standard. You should understand what's nonstandard about it, but dialogue is what a character says, and if that character has poor grammar or uses a dialect that the grammar checker can't handle, so be it. As a side note, I find it unlikely that your characters are truly using passive voice. Do you have examples? It seems much more likely that the grammar checker is incorrectly diagnosing passive voice.
As Cog says, grammar checkers are not yet able to cope with the complexities of normal English. At their best they will push you towards a simplified sort of English that they can parse. At their worst they will try to change your meaning altogether. That said, I do tend to work with grammar, style and spelling checkers turned on. But when they flag something up I don't simply accept it; I work out why the checker is objecting and make my own decision about whether the objection is a) correct and b) relevant.
i also keep it on... but rarely bother to check out why something has been squiggled, since i can see for myself if it's a typo or something recognizably needing correction... if it's neither, i may take a quick look at the reason, but next to never agree with it...
I was afraid I would get more info than I really needed but I have been pleasantly surprised. I wish I could have found such great advice and support 50 years ago. Thank all of you for your answers. Down here the real "Suthrn" folks would say "Ya'll are so nice."