Deep within the narrative, mingling with other heavier aspects of Story and sinking to the bottom of the Word-Pond is theme. A fundamental underpinning of the story, theme can be a tricky fish to get a grip on. Theme is a subtle aspect of any written work. It is rarely stated in a bald fashion, but even if it isn’t obvious, theme is a unifying thread that goes through the story from beginning to end.
According to Wikipedia:
A theme is different from the subject of a work. For example, the subject of Star Wars is “the battle for control of the galaxy between the Galactic Empire and the Rebel Alliance.”
The themes explored in the films might be “moral ambiguity” or “the conflict between technology and nature.” 
In other words, theme is what the story is about on a deeper level than what is seen on the surface. It’s the big meaning, a thread that is woven through the entire story, and sometimes it is an unstated moral for the reader to infer.
I’ve said this elsewhere, but theme is an idea-thread that winds through the story, supports and gives meaning to the plot. On the surface, each of the different commercial literary genres looks different. Each genre is deliberately tailored to fit a wide variety of niche readers. Yet, from shelf to shelf, we will find commonalities, themes that all stories tell in one way or another.
Genre is the bookstore label guiding a reader to the shelf containing books they are most likely to enjoy.
But some aspects of Story are universal and independent—they roam through all the genres from children’s books to literary fiction and connect them.
Theme is a universal feature of Story.
We all recognize Romance as a theme. It can be the major theme or a supporting theme. Romantic love is a defining feature of the genre of Romance. But what are some different aspects of love that can be found in every genre from fantasy to sci-fi, to horror, to crime fiction?
- Love gained (the fairytale romance)
- Love lost
- Tragic love
- Selfish love
- Brother/Sisterly love
- Dangerous Attraction
- Parental love
Love is only one theme despite the fact an entire genre has been built around it. Others abound, large central concepts that build tension within the Story.
Here is a brief list, just a small jumping off point for your creative mind. Some are large themes that entire genres have been built around, and others are good supporting themes:
- Separation and reunion
- Nostalgia for the good old days
- Fall from Grace
- Rebellion and revolution
- Coming of age
- Crime and Justice
- Midlife crisis
- The hero’s journey
- Humanity in jeopardy
- General dehumanization of society
- Good vs. Evil
- Religious intolerance
Again, Wikipedia, the fount of all knowledge, offers us wisdom:
(Theme) can often be summed in a single word (e.g. love, death, betrayal). Typical examples of themes of this type are conflict between the individual and society; coming of age; humans in conflict with technology; nostalgia; and the dangers of unchecked ambition. A theme may be exemplified by the actions, utterances, or thoughts of a character in a novel. An example of this would be the theme loneliness in John Steinbeck‘s Of Mice and Men, wherein many of the characters seem to be lonely. It may differ from the thesis (hypothesis; idea)—the text’s or author’s implied worldview. 
Sometimes we can visualize a complex theme but can’t explain it. If we can’t explain it, how do we show it? Consider the theme of “grief.” It is a common theme that can play out against any backdrop, sci-fi, or reality based, where there are humans interacting on an emotional level. When you see a dog grieving the loss of her mistress, or a husband grieving for his wife—what do you see? You can’t read their mind, so you must look for clues. What behaviors inspire empathy for their sorrow in you, the observer?
Highlighting a strong theme can be a challenge if you begin without a plan. A plan is not always required because, in some stories, the flash of inspiration we begin with is a strong theme. The theme develops as you write, and immediately, you see what it is. In my case, I need a plan fifty percent of the time.
Whatever the case, once you have identified the main theme, you can write the story in such a way that it is shown through:
- Symbolic settings/places
- Allegorical objects deliberately placed within the setting
Other times, it is difficult to decide what the underlying theme is, and the story is weak. It has no legs and won’t ring true until you find out what the underlying theme is. This requires a little mind-wandering on your part. You must ruminate on the character’s quest or dilemma. Ask yourself what the root cause of the issue is—if it is a crime, why is crime rampant. Is it a societal problem? If the core dilemma is unrequited love, what are the roadblocks to a resolution?
Themes exist in every story. However, when we are first laying down the story, themes are like your drunk uncle—they hang out in the bar until closing time when they have to weave their way home through dark alleys and the neighbor’s shrubs. When you have finished your first draft (closing time), if you still haven’t found the defining theme, look in the local bar in the first chapters for clues your subconscious mind has sprinkled throughout the story. If you still haven’t got a theme, pick one and develop it.
At the surface level of the Word-Pond, each genre looks widely different. But when you go deeper, you find that all literary genres have one thing in common: they have protagonists and side-characters who all must deal with and react to the underlying theme of the book.
Credits and Attributions:
 Wikipedia contributors, “Theme (arts),” Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/w/index.php?title=Theme_(arts)&oldid=848540721 (accessed July 27, 2019).
 Wikipedia contributors, “Theme (narrative),” Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/w/index.php?title=Theme_(narrative)&oldid=765573400 (accessed July 27, 2019).
Photograph, McLain Pond in July, © 2018 by Connie J. Jasperson, from the author’s private photos.
Worked to Death, H. A. Brendekilde. Wikimedia Commons contributors, “File:H. A. Brendekilde – Udslidt (1889).jpg,” Wikimedia Commons, the free media repository, https://commons.wikimedia.org/w/index.php?title=File:H._A._Brendekilde_-_Udslidt_(1889).jpg&oldid=355191092 (accessed July 16, 2019).