Logically, there is no need for chapters in novels at all. You, the writer, could start the book on page one and keep going right to the end...
Some commentators argue that novel chapters, being the artificial divisions they are, detract from the sense of reality that writers try to create.
I would argue that the audience is perfectly aware that novels are "made up" stories...
If the readers are able to imagine that the characters and events are actually real, dividing the novel into chapters really isn't going to interfere with their "willing suspension of disbelief."
On a more practical level, the reason books are divided into chapters is largely to do with making the experience of reading the book more user-friendly.
Give the audience plenty of "resting places" and you will keep them happy - assuming the words in between the rest stops are any good, of course.
As few or as many as you like. Some novels contain 50 or more and some (extremely rarely) contain none. The average seems to be about a dozen.
They can vary in length between just a couple of pages and 50 or 60. Somewhere around the 20-page mark is about the average.
(Incidentally, you have probably already divided your novel into chapters using your instincts. This is a good way to do it. But you might want to use the information here to check your choices and perhaps make any small adjustments.)
Usually, insert a chapter break when a scene ends and an interlude begins. Or, to use the terms I used in the article on plotting the novel, when the "action" phase of a mini-plot ends and the "reaction" phase begins.
But there are no hard and fast rules here...
Perhaps the best advice is simply to end a chapter where your instincts tell you to end it - by which I mean at a place where a break feels natural, where the questions the readers had at the start of the chapter have been resolved and new questions have been raised in the readers' minds about what will happen in the next chapter.
What about mini breaks within chapters?
Mini breaks are the ones denoted by a line of white space, or perhaps by asterisks if they occur at the end of a page. Again, they are not necessary but they help the reader. (They are a good place to "put down anchor" for the night if you can barely keep your eyes open and the end of the chapter is too far ahead.)
Some novelists use them and others don't - the choice is yours. Trust your instincts and use them wherever a pause feels natural.
Don't include a break in the middle of an action sequence (unless you are switching from one viewpoint character to another, perhaps). But if you have a shift in time and space - "One hour later Mary was back home..." - and you are not starting a new chapter, a break would be a good idea.
Some novel writers give their chapters a title, others don't. I have chosen to title the chapters in my current novel - beginning with "Chapter One: The Insecure Angel" - but there is no logical reason for this. I just felt like doing it!
Here are some of the many ways I could have titled my chapter...
Adding titles to chapters, I believe, adds another small element of interest to a novel. The individual titles whet the readers' appetites for what is about to come. On the other hand, most writers don't bother with them.
(Please see the article on titles in novels for specific advice on this.)
If dividing a novel into chapters is largely a way of making the reading experience a more user-friendly one - by creating white space and resting places - the same is not true for dividing a novel into parts.
The purpose of splitting a novel into parts is really a method of separating radically different sections of the novel. What do I mean by "radically different"?
Note that these differences should be sudden, and only happen once or twice.
Only divide a novel into parts if there is a sudden leap from 1954 to 1978, and then from 1978 to 2010. If Part One actually covers the entire 24 year period up to 1978, there is no need to suddenly have a new part, because time has been steadily advancing throughout.
If the New York-London novel has the character jetting across the Atlantic frequently, don't bother with parts, because the reader will be used to these shifts in place.
And if the changes of narrator occur frequently in the love story - every chapter or two, say - you don't need parts. Parts are only there to warn the reader that a major shift (one they have not experienced before) is about to take place.
Parts, like chapters in a novel, can be titled or not. There are three main options here...
The first thing to say is that if you have no good reason to include a prologue in your novel, don't.
The opening of a work of fiction is all about hooking the reader and keeping them reading - and prologues, however exciting or crucial to the story they might be, are still a barrier that the reader has to get beyond before the story-proper begins.
A prologue is a kind of pre-story, informing the reader of some event from the past that is necessary to understand the present...
So if a novel is about a year in the life of a man, say, the prologue might deal with an event that happened when the man was 12 and that continues to affect him.
Or if a novel begins with discovery of an Egyptian tomb, the prologue might take place thousands of years earlier when the king was buried.
If you believe that writing a prologue is necessary, write one (they are common enough in novels). Though it is a good idea to keep it as brief as possible. If you have some crucial backstory to get across but believe you can work it into the main body of the story - in the form of a flashback, say - do that instead.
Sometimes a prologue is literally entitled "Prologue". More often, it appears as a few pages of italicized text with no title (the fewer the number of pages, the better) before Chapter One begins.
Now for epilogues...
Here, you no longer face the problem of keeping the readers interested. If they have made it to the end of the novel, they aren't going to close the book at the start of the epilogue and demand a refund.
Epilogues, however, are extremely rare in novels, and that is probably all the reason you need not to include one.
Epilogues deal with the aftermath of a story. I don't mean the immediate aftermath, because all novels deal with that - either directly or by implication. I mean what happens to the characters 5, 10, 20 years after the novel's events have finished.
The question is, why would you want to show this?
What do I mean by "adds something"? Simply that your exploration of theme and character and so on should be enhanced by the addition of an epilogue, not dragged down by an unnecessary one - and the only way to tell that is, as always, to trust your instincts.
If you still aren't sure, forget all about writing an epilogue. They are so rare in contemporary literature that the reader is hardly going to miss one.
Nineteenth century novels sometimes ended with an epilogue, but they really aren't going to help you write a modern one.
If you wish to see what a contemporary epilogue looks like, try John Irving's The World According to Garp (it is the only modern novel I can think of with an epilogue).
You can make up your own mind whether the novel would have been just as good, or even better, without it.
Related Article: How to Find Titles for Novels.