What is theme? Theme is all the core concepts of your story, distilled down to their best words and organized into a best sentence. And just like always I have a snazzy chart and system to explain this.
Step 1: Describe Your Manuscript/Creation/Baby/Whatever You Want To Call It
Compose as many sentences, phrases, words as possible to express to another human being what your writing is about. Don't tell them about the plot, or the potential plot, I mean talk to them about the vibe, mood and feel. (Yes, this is where a "Feel" Document can do double-duty). Let's put together a few examples:
1. The Dresden Files RPG
- often darker than intended
- going H.A.M. (google it adults) is encouraged.
- Magic, grit and not always a bright sunny conclusion
- There's a whale
- Revenge is a dish best served with a harpoon
- When in doubt, carve your coffin
- Get used to the rhythm of the sea
- Don't be a wuss, move your back row
- Only 2 players
Go through your lists (or your Feel Document) and craft a sentence that either quotes those items you listed in Step 1 or paraphrases them. You don't need to force yourself into a single sentence, but don't take that to mean that you couldn't go overboard - you want less than a paragraph here. To our examples!
1. The Dresden Files RPG - Magic is real, wizards and the supernatural are alive and kicking, and sometimes you have to suffer to succeed.
2. Moby Dick - Obsession will kill you.
3. Checkers - Forward progress is a good thing.
Step 3: Find the Power Word in the sentence(s) you just wrote
A 'Power Word' is the word or word-phrase that carries all the emotional or impactful weight of a sentence. It's often the word that draws the eye and imagination and leads the reader to nod their head and "get it". It sometimes takes practice to find the best word, or to narrow it down from a few potential words to one definite choice, so I advise you to try these three steps for a lot of writing, not just your own, until you get into the habit. Onto our examples:
1. The Dresden Files RPG - "Suffer to succeed"
2. Moby Dick - Obsession
3. Checkers - Progress is good
Step 4: Success!
That power word or phrase is your theme! Congratulate yourself.
Note: Theme isn't 'wrong'. If you would look at each of those items and draw together totally different words, sentences and themes, great! Theme is subjective, and it should be. However, should we compare our notes, our themes should be in somewhat of the same range (we're both a litte pessimistic, or they're both character-driven or they both relate to another particular idea or even that they're polar opposites on the same spectrum) else we're only going to conflict with each if asked. And maybe, that conflict is okay.
Note 2: If you can't identify a 'theme' you're missing out on a powerful selling point, and a powerful building block for your manuscript going forward. Theme is often a lighthouse that you can navigate by, and return to when you end up astray in the middle of Act 2 and you have move things forward towards climax. Or in game design, theme is one of the great "sinews" that ties mechanics to setting in a way that appeals to a player on a level beyond "Ooh I get to roll the blue dice!"
Because it's so strong and so intense, I put theme at the top of the writing pyramid. And maybe you should too.