@samuel Yes. Basically, the more complex your novel, the more themes you can have in it.
Any novel you pick up will have multiple themes. When we talk about a story’s theme though, we generally mean its main theme. A novel generally has one main theme. On some occasions it will have two or three main themes, but this is not common. You can have lots of supporting themes, but you generally have one main one.
You have your main theme, then you have all the little facets of the main theme.
I’m a big stickler for continuity, so of course I’m going to recommend you only have one theme, but…
One theme can have a lot of facets.
Or, to put it another way, one theme can be shown to be true many different ways.
For example, in Zootopia they show a lot of different ways that any animal can be anything. Or: The Dark Knight Trilogy shows a lot of different ways that people are basically good… even though some people just want to watch the world burn.
Wreck-It Ralph, Megamind, and Despicable Me show how just because you’re a bad-guy, doesn’t mean your a bad guy.
Or you might have a faux theme.
I recently read Steelheart by Brandon Sanderson (which is an amazing book, by the way), and it seemed like it was going to be about revenge, but it didn’t end the way a story about revenge should have. Then I read the sequel, and the theme for the trilogy is completely clear now.
I won’t say what it is because that would give away spoilers.
But it’s almost like Steelheart had a faux theme. Something to distract you from the real theme so that story elements from the sequel wouldn’t be revealed.
Of course, this would be incredibly hard to pull off. And perhaps the fact that Brandon Sanderson does it is proof that you shouldn’t try it at home. 🙂