Our central thesis is that science fiction consists of speculative fiction set in a naturalistic world. First, let’s define our terms:

Speculative fiction

Speculative fiction is counterfactual fiction — fiction that assumes the world is different than what it currently is. For example, speculative fiction may assume that the earth is flat, or that the year is 2120, or that technology makes it possible for us to download people’s memories, or that the Nazis won World War II. In short, it deals with worlds that are notably different from the world you and I face in our day to day lives. Speculative fiction involves plausible extrapolations of known or plausible technology (like virtual reality or hover cars), or totally implausible technology (like warp drives and transporters). It could also involve no technology at all, such as alt-history literature.


For our purposes, naturalism is a worldview that treats the operations of the universe as though they are reducible to (1) inert matter, energy, or space-time (2) governed by universal rules.[1] This definition has two parts. The first describes what exists in the universe, and the second describes the rules of the universe. Let’s explore each in turn.

(1) The world consists of inert matter, energy, or space-time.

One way of putting this is that a naturalistic universe omits the presence of the “supernatural”. Note that we aren’t referring to things unexplained or mysterious, as is sometimes meant by supernatural. Rather, we are using the term as it is often used in colloquial conversation (but rarely defined):[2] The supernatural is metaphysically different from what is “natural,” because it inherently involves things that are not reducible to the operations of inert matter, energy, or space-time. For example, any set of rules that involve language, intent, aspiration, or teleology at the substrate of the universe is inherently supernatural.

You might find emergent properties such as intelligence, meaning, language, etc. in a naturalistic universe — but a naturalistic world assumes that all of these are reducible to more fundamental arrangements of matter and energy passively complying with universal law. Richard Carrier refers to these emergent properties as “mental things” (the type of things we associate with the human mind), and explains, “’[N]aturalism’ means, in the simplest terms, that every mental thing is entirely caused by fundamentally nonmental things, and is entirely dependent on nonmental things for its existence.”[3]. (For our purposes going forward, we will sometimes use Carrier’s “nonmental” term to describe this property of naturalism.)

(2) A naturalistic universe is governed by a set of universal rules.

The rules of a naturalistic universe have a few specific characteristics:

  • They are universal. If a rule or pattern varies across time and space, naturalism assumes that there is a more fundamental natural law that accounts for that change.
  • They are unchangeable. Not only do they not vary across space, they do not vary across time. Nor could they be altered or tweaked. They are what they must be.
  • They are passive. They can only await discovery. They unfold as they must, and intend nothing at all.
  • They are impartial. The physical world will run the way it runs, whether or not we are there to witness it, and no matter who we are.
  • They are morally neutral. The universe and its rules are neither good nor bad. If morality exists at all in a naturalistic universe, it exists in the minds and preferences of the sentient beings who live there.

In other words, in addition to involving things that are not reducible to the operations of inert matter, energy, or space-time, the supernatural can involve world-building or processes that violate the above characteristics in some way. A supernatural rule, for example, is one which has its origins in the will or mind of a person — which implies that it could change across space or time by will. A supernatural rule could also be the product of a will on the part of nature itself, a nature that is neither impartial nor passive. Naturalism negates or omits the supernatural in all of these varieties.

Note that impartiality implies being impartial both between specific observers, and between observers and no observers. To answer the age-old question: if a tree falls in the forest and there is no one there to hear it, does it make a sound? Naturalism says yes, to the extent that sound consists of percussive waves through the air that could have been detected by sentient beings had they been there. Further, one implication of the passive and impartial features of naturalism is that anyone who documents the empirical world and analyzes its patterns with sufficient skill can unfold the laws of nature. Success in science relies entirely on method, not heritage, intention, or fate — the universe does not care who attempts to unlock its secrets. The passive rules of the universe do not care how we live, or what we do with our knowledge.

Speculative fiction in a naturalistic world

Science fiction describes the intersection between speculative fiction and naturalistic world-building. Speculative fiction that does not take place in a naturalistic world is not science fiction (and is likely fantasy). Further, non-speculative fiction that does take place in a naturalistic world is not science fiction either — it could, for example, be a romance, a mystery, or a thriller. But when speculative fiction meets naturalistic world-building, we have bona fide science fiction. We can think of the above characteristics of naturalism as the “flags” of science fiction. Speculative fiction that flies all of these flags is very likely to considered science fiction. If any one of these characteristics is violated, the work is likely to not be treated as science fiction.

It should be noted up front that naturalism does not have a monopoly on science. Science involves rational analysis coupled with systematic observation, but does not require that the world look the way we describe above. Those living in a non-naturalistic world might find rational analysis and systematic observation to be equally powerful tools for exploring their world.[4] Science fiction, however, has evolved so that (today) its contours are almost entirely coextensive with those of naturalism.

Alt-universe science fiction

Nothing about this definition requires that the laws of a science fiction universe resemble our own. In fact, in some science fiction universes, they don’t. In “soft” science fiction, the rules often violate known science. We usually sweep this under the rug by saying, “Maybe we will figure out how to do this someday.” But under our definition, we don’t have to pretend that known impossibilities are the product of future innovation. The rules can straight-up be different from what we know or think to be true about the world.

Further, this might mean that an ostensibly fantasy universe could qualify as science fiction, if its magic system has been developed as though it were a set of naturalistic rules. For example, if creating a potion merely involves putting the right plants and ingredients together, and could be replicable by anyone at any time in any place with those same ingredients (regardless of their intentions), then you might merely have an alt-universe chemistry as opposed to magic. In such a world, you could build a recipe book of spells the same way we’ve fleshed out the periodic table. It is a naturalistic universe, even if it is counterfactual to our own.

One could therefore create a universe with dragons and castles and mages, and it could still be entirely science fiction (of an alternate universe variety), if the dragons are a product of natural selection, or the mage’s magical abilities are the product of his systematic observation of the universal rules of his universe — even if those rules are drastically different from the rules we are familiar with in our own universe. All it requires is that those rules adhere to the characteristics of naturalism listed above: they are universal, unchangeable, passive, impartial, and morally neutral, and govern a world of otherwise inert matter or energy.

References   [ + ]

1. There are other definitions of naturalism that are useful in other discussions. This is the definition we are using for the purpose of this series.
2. Richard Carrier argues that this is the colloquial usage of the term here: Richard Carrier, “Defining the Supernatural,” 18 January 2007.
3. Richard Carrier, “Defining the Supernatural,” 18 January 2007.
4. In fact, this is the worldview of Christians around the world: we live in an inherently non-naturalistic world in which God is a creator (who is not reducible to matter or energy passively following universal laws), but yet systematic observation and rational analysis are indispensable assets for illuminating their universe.