|I ain't gonna 'splain it all to ya today.|
We recently covered those damned dialogue tags, which definitely have rules. Now let’s look at dialogue itself, where rules go to die. A fellow writer posted up this question:
So a teenage boy walks into a cave and says, “There's bones everywhere.” Or does he say, “There are bones everywhere.” I'm not wondering which is correct. I'm wondering which you think a boy would say.
If you want grammatically correct, “There are . . .” is the right way to go. But that’s as far as advice can take you because of the degree of unknowns about this character. Is the character highly educated or highly intelligent or given to speaking in a very robotic what? Even those of average intelligence and modest education might speak in such a way to make themselves sound more so. Whereas a character adopting a persona might "dumb down" the speech and use "there’s” improperly on purpose. The decision tree branches out so quickly, we can’t make an accurate map.
What's important is to write to your audience and in such a way that your speech and your narrative flow. If you want the character you created to sound more human than grammatically correct, then he could say it anyway you wanted. Samuel Clemens/Mark Twain was a master of the nearly indecipherable, grammatically incorrect, but colloquially perfect dialogue:
“Right is right, and wrong is wrong, and a body ain’t got no business doing wrong when he ain’t ignorant and knows better.”
The Adventures of Huckleberry Finn
Spoken dialogue does not have to adhere to the same grammar structure that other writing should (normal caveats apply). Of course, you need to know the rules first so that you can break them correctly. Otherwise, like a poor diamond cutter, you end up with a giant inconsistent mess. As long as you are consistent in speech and the speech flows, and you understand what rules you're breaking and why, your dialogue can read anyway you need it to.