A theme is an existential inquiry. And increasingly I realize that such an inquiry is, finally, the examination of certain words, theme-words. Which leads me to emphasize: a novel is based primarily on certain fundamental words. It is like Schoenberg’s “tone-row.” In The Book of Laughter and Forgetting, the “row” goes: forgetting, laughter, angels, litost, border. Over the course of the novel, those five principal words are analyzed, studied, defined, redefined, and thus transformed into categories of existence. The novel is built on those few categories the way a house is built on its pillars. The pillars of The Unbearable Lightness of Being: weight, lightness, soul, body, the Grand March, shit, kitsch, compassion, vertigo, strength, weakness.
–Milan Kundera, The Art of the Novel (85)
I like this idea of theme-words. One might also translate it to images.