Writing Speculative Fiction--Part I: What is Speculative Fiction?

I'm going to do a series of posts on speculative fiction for a class I'll be teaching at an upcoming writing conference. Hope you all will find some value here!

Speculative fiction, according to Wikipedia, is: "an umbrella term encompassing the more fantastical fiction genres, specifically science fiction, fantasy, horror, supernatural fiction, superhero fiction, utopian and dystopian fiction, apocalyptic and post-apocalyptic fiction, and alternate history in literature as well as related static, motion, and virtual arts."

In other words, speculative fiction is the type of fiction that speculates about something contrary to our known reality. Speculative fiction answers the question, "What if?". 

What if we had faster-than-light space travel?

What if aliens visited Earth?

What if magic were real?

What if dragons existed?

What if a natural disaster destroyed civilization as we know it?

The possibilities are limitless, once we willingly suspend our disbelief. I think that's why I love reading, watching and especially writing speculative fiction so much.

What are your thoughts on what constitutes speculative fiction?
Up next: Part II: The difference between science fiction and fantasy