Themes...hmm, well, themes aren't what you see listed as themes all over the place such as paranormal or cowboy for romance novel "themes". Themes are the underlying idea the author is trying to convey. It's not easy to define, and no, sorry, there isn't a master list of themes any more than there is a master list of ideas humans can have. Sometimes the author may not even be really aware of what idea is driving them or underpins their story, but the smart writers try to identify the major theme in their work and strive to make sure the story and every scene in the story supports and enhances the theme.
Themes are the difference between a fluffy novel that you enjoy and promptly forget the next day, and novels which resonate with the reader long after they have finished it. Sure, you can "get away" with not developing a theme, but you're missing the main method we have to write something with depth, something that will live long after we have turned to dust.
I've avoided tackling themes because they really are hard. They hard to identify and they're one more crafty-thing we have to think about when writing our stories, which can already be a daunting task even without trying to work out themes. But it is truly worth the effort.
For me, the theme underpining much of my own work is the importance and responsibility of individual freedom--the more Society tries to control and restrain individual freedom, the more hostile the environment is to innovation and progress, however, individual freedom does not mean behaving badly or attempting to destroy the Society in which one lives. It is a delicate balance but an important one. I firmly believe in responsible, individual freedom.
One note: it is important to differentiate between themes and subjects. A subject is what something is about, like Dickens writing about child labor, while a theme is what the author thinks about it, i.e. that child labor is shameful and ought to be eliminated. That's why it can be so hard to precisely articulate a theme, because it is the what the author feels and thinks about a specific issue, not just the issue itself.
If you can identify the subject and then state what the author thinks about it, you've got a theme. Another tipoff is the word "that". You'll notice I used the word "that" when I finally described the theme: Dickens often wrote stories showing that child labor is shameful and ought to be eliminated.
So, in my continuing efforts to improve my own writing, I'm going to explore themes.
First, let's talk about what are not themes.
Romance, Mystery, Suspense, Science Fiction, Chick Lit, Paranormal, Mainstream: These are genres, not themes.
Cowboys, vampires, fairies, elves, werewolves, hidden baby, reunion, plump heroines, Irish, Regency, Scottish, Sweet, Historical, Time-travel: These are all "handles" for types of romance novels, created so readers can find the stories containing the situations and/or characters they like best.
Now that you know what are not themes, lets look at some themes. The interesting thing about themes is that not all readers will agree on exactly what idea, or theme, the author had in mind when they wrote the book. That's why English majors can write doctoral theses endlessly on the same novel(s) and they can all be right, because different people will digest the really big themes in slightly different ways, and as I pointed out earlier, the theme is what the writer thinks about the subject, which makes it subjective.
Readers can more easily articulate the subject, e.g. the plight of the Colonists before 1776, but the theme is whether the writer thinks the Colonists were a bunch of cry-babies who would have been better off under British rule, or if the writer believes the Colonists did the right thing by breaking away from the idiotic tyranny of the Empire. It's the slant or position taken that differentiates the theme from everything else. Yet another reason it is so hard to write any kind of guidance about themes or give a list to anyone. That said, I'm going to take the plunge and give two examples.
We'll start with Ayn Rand's Atlas Shrugged. Rand was obsessed with a lot of things, but after reading this particular book and having it resonate deeply, I, personally, decided that to me, one of the themes in this book concerns the tyranny of the mediocre. The main characters in this book are basically what you might consider over-achievers who, if allowed to do so, could provide the world with products that would improve everyone's lives. However, instead of being given the freedom to expand their business, create new products, and generally improve mankind's lot, the other petty, mediocre characters held them back and placed obstacles in their path. Every scene in this book built upon this theme of brilliant, innovative ideas being held up or destroyed by people who didn't want anyone else to get ahead. In the end, however, innovation succeeds and is its own reward.
If you want to know why this theme resonates with me, I can give you one real-life example of the theme in action. My grandmother was working in a factory during WWII. Taking great pride in her work, she did as good a job as she could. After her first week in the factory, her co-workers "met her" in the lunch room and told her if she didn't slow down they would break her arms because she was making the rest of them look bad. Tyranny of the mediocre. That's one theme and one interpretation of that theme.
As you can see, it is easier to identify a theme if it has some meaning in your life. If an author's theme does not have any particular meaning to a reader, they will most likely be unable to identify it clearly. That's why I think it's so hard for young people to get a handle on themes in the literature they are forced to read in school, because they have limited life experience.
However, being unable to articulate a theme is actually quite alright. At a minimum, if you can give the reader a good story, they will love it despite not "getting" the underlying theme. They may not even be aware that they are missing what is under the surface.
The thing is, even if the reader doesn't consciously "get" the theme, by making sure your story has a consistent theme underpining it, your story will be stronger and more memorable. It will lend the story an internal consistency and skeleton which, although unseen, will give it legs and carry it where "weaker" stories can't go. Chances are good, your characters and your story will be the ones the readers will remember.
Let me give you another example of a strong theme. Again, this is how I understand the theme. Your mileage, as they say, may differ. Do you remember the Charles Bronson Death Wish movies? Now there is a strong theme. When Society's justice system fails, you must take justice into your own hands. In stating that, I consciously avoided the use of the word revenge even though I desperately wanted to say: Revenge is sweet. Although Bronson's character suffers mightily in meting out justice in an unjust society, there is an underlying message that this is necessary to bring order to Society, even if it does not ultimately bring the hero happiness. It's difficult, actually, to say whether the hero is at least satisfied at the end--although as a viewer of the movie, I'd have to say the audience is expected to be satisfied when order and justice prevail. I'm certainly satisfied.
Tolkein's Lord of the Rings trilogy has been analyzed ad nauseum, but the themes in it that resonate with me are those of duty and self-sacrifice. That it is important to do the right thing even if it means you may die trying. Frodo must carry the ring and try to destroy it, even if it means his personal destruction. Star Trek fans may recognize this same theme in Spock's memorable statement: The needs of the many outweigh the needs of the few.
Sometimes, self-sacrifice is necessary.
I realize I've really only talked about two themes, but as you can see, they are as varied and numerous as the stars and just as difficult to describe. You may completely disagree with me on even just the two I've mentioned, and that's okay, because that's the power of Themes: personal interpretation.
This brings me to one more tip about Themes: at some point, and usually at several points, your characters should and probably will state your theme, just as Mr. Spock did.
Gertrude Stein's Three Lives contained a story about Melanctha who stated a theme, if not the theme, in no uncertain terms. You have to know what you've got, when you've got it. I read that story 30 years ago and still remember it. I still recall that line from it, being repeated by Melanctha several times, because although she said she knew what she had when she had it, she still lost it. Think of the power of that writing if I can remember it 30 years later without having opened the book again since school days.
Identifying your theme and ensuring that your character's state it gives your readers the keys to the kingdom. It will make them catch their breath and remember not only that specific line from your book, but your entire book. It is what will catch at them years later and may even influence the way they see the world. It is the power of storytelling.
Don't ignore the power. Take hold of it and use it.