When you think of the most famous time travel stories, invariably your mind lands on a machine: Wells’ original Time Machine, Doc Brown’s DeLorean, the Doctor’s TARDIS. Whether those machines are propelled hundreds of centuries forward, or land in the recent past before heading back to the future, or simply bounce around in wibbly wobbly timey-wimey, they’re carrying their intrepid time travelers all across space and time, freeing them from linear time.

So—time travel occurs via technology and/or science, which allows us to peek into the future. Sounds like science fiction.

Except.

In Outlander, visiting the standing stones at Craigh na Dun at a particular time sends Claire backwards in time 200 years, to 1743 and a new love interest despite being married in 1946. Whenever Dana gets injured in 1976, she returns to the same plantation over the early 1800s, compelled to interfere in the goings-on of a slaver family in Kindred. And The Ancient One has young Kate happen upon the ominously named Lost Crater and its grove of incredible redwood trees only to be propelled 500 years in the past, where she wields a magic staff and helps an extinct civilization fend off a giant volcano creature about to blow.

Three time travel narratives that not only include no technology but also contain no real method for time travel aside from an ineffable magic.

So… is time travel fantasy, then?

It’s a question I thought I had an immediate answer for, but the more time travel narratives I consider, the more difficult they become to categorize. The “how” of time travel, at least, seems straightforward enough:

Machines, vehicles, genetic or mutant powers, wormholes, tesseracts, devices… science fiction.

Magic, spells, mystical artifacts, time turners, ancient beings, multiple lives, whole buildings, or simply no explanation offered… fantasy.

But even that attempt at a taxonomy is fraught, as it just creates more questions: Isn’t a time turner technically a device? Is it merely the magic that powers it that distinguishes it from something like the DeLorean’s flux capacitor, which runs on…

Well, it’s not actually clear what that runs on. This special box is responsible for “flux dispersal,” but that still doesn’t actually answer why 88 MPH is the target speed, or how the DeLorean jumps through the space-time continuum. It’s just one of those things that the writers of Back to the Future handwaved away, and we just accept that that is how time travel works in that particular universe.

So how much “science” do we need for time travel to be science-fiction? Even aside from time travel narratives, some sci-fi will go always the handwave route, while others create hard rules for the technology or science propelling the story. Take, for instance, the divide between Jules Verne and H.G. Wells. Ditto for fantasy—writers can create in-depth, multi-layer magic systems with clear conditions and consequences, or describe a magic that just is. How do you have any hope of categorizing time travel as one genre or another when there seems to be so much gray area, when very little about it seems clear-cut?

Even though you would expect time travel to require hard rules, it seems to most often appear in both science fiction and fantasy stories that require a certain amount of handwaving on the details. We’re given some sense of how the TARDIS operates—the chameleon circuit, and the sometimes-isometric, sometimes-telepathic controls—but it’s best just to jump in and hang on. Similarly, there’s no clear explanation for the time travel in Kindred or Outlander aside from supernatural forces working outside of our understanding or control, forces that cause certain events to occur as part of some larger cosmic plan.

Regardless of genre, it seems, time travel is often treated like magic. So why does it feel easier to think of time travel stories as science fiction? And where do you fall in the sci-fi-versus-fantasy divide?