So now that we have the official definition, what does this mean?
A paragraph is a self-contained unit of writing dealing with a particular point or idea. Most of the time, I use this definition to mean one person, be it action or dialogue = one paragraph. I say 'most of the time' because that's the way it is most of the time, but not always. Ever once in a while, you'll get a character who takes off on a very different subject or action without having been interrupted by any other character's paragraph. In dialog, this usually occurs when one person is trying to explain some rather wide subject. This is shown by starting the new paragraph (same speaker) with quotation marks without having closed the last paragraph with quotations. If you ask me, this is a situation that should be avoided, and it can be easily enough. You can break up such a long discourse with action, either by the speaker or by those who are listening, or even by external interruptions if appropriate.
On the opposite end of the spectrum, paragraphs can be as short as a single word of dialogue. In a page full of dialogue, it's not uncommon for one person to contribute a single word as their part of the conversation. A long string of this sort of dialogue is also something to be avoided. No one want's to read pages filled with too simple dialogue, so don't be afraid to cut to the chase as quickly as possible.
Dialogue, no matter how long or short, begs a mention about tags, something I've posted about before. I like to keep actual tags to a minimum, and the wide variety of tags should be avoided. Your story would be much better if all the flowery tags were instead bits of action.
In fiction, each paragraph serves to advance the plot, develop a character, describe a scene, or narrate an action. This means that each paragraph should follow the last one in a clear logical progression of action. A paragraph is also a single entity. One person, be it action or dialogue should be contained in one paragraph, though there are a few exceptions.
In the interaction of say two characters, each person's action and dialogue should be included in a single paragraph, and when the next person adds their part, start a new paragraph. Avoid attaching the reaction of one character onto the end of another character's paragraph. Consider each paragraph as a character's personal space. You know how bad it is to invade personal space?
Clues to indicate a change of scene or the passage of time without really changing the action much can be a single vacant line. However when a scene as well as action change takes place, it's best to add a chapter heading here.
Example of the passage of time:
Despite his recent terror and pain, Derrick sighed and closed his eyes. He didn’t see the gentle glow that passed between the man’s hand and his own body as he fussed over him. The glow was so faint that it wouldn’t have been visible at all, if it hadn’t been a moonless night.Nothing happened during the night so the jump in time was shown by a blank line. Not to have this blank line would end up feeling like a run-on sentence, all shoved together, no moment for a channel change (yes, sometimes our brains need a moment to change channels).
Derrick did feel better the next morning though far from great; his head was still splitting and his right eye was swollen shut.
Example of a change of location without really changing the subject of the chapter at this point:
The outside perimeter of the circle was obscure among the forest, but not all that difficult to find, now that he knew what to look for, so he walked that circuit too. Strangely enough, his trail appeared to have found the only entrance to the grove. Any others must have been closed off by being heavily trapped or perhaps it was merely the turning of the ground that had discouraged any trails accidentally penetrating into the core of the grove. Any magical traps were nonexistent; Derrick wasn’t too sure if any spells would have survived the death of the caretaker anyway.At this point, both Derrick and Aramil are living in the same house but they are in very different locations at this point. Derrick is exploring the grove not far from his house while Aramil dozed elvish style. Not to have this break makes the reader want to put these two locations too close together. Kinda like someone slammed one door in your face and rammed another one open onto your toes. Rather painful.
Back at the house, Aramil was still sitting on the one stool leaning against the cabin’s wall; he hadn’t moved a muscle. Derrick filled the table with fruit, steaming vegetables and hot bread; it was the creation of a steaming ham that roused Aramil from his pseudo-slumber. He chuckled. “I didn’t pay much attention back at the gathering, but I’m thinking you’re not a vegetarian.”
A chapter break can and should accomplish nearly all of the kinds of breaks, change of scene, passage of time, and change of location, in one leap.
One day, nearly six and a half weeks after their return from moot, Derrick once again suspended their normal routine, declaring that it was time to give thanks to the Lady for bringing spring. Following an old trail, they hiked above the treeline where they lit a fire in an already established, though neglected fire pit. “Gifford must have come here too,” said Derrick as he brushed the leaves out of the stone-lined bowl.The above is the beginning of one of my chapters. As you can see, A span of time has passed, and a change, even though temporary, was planned in both scene and location.
So a paragraph, to a certain degree, is a character's personal space. Mind your manners and maintain your space.