The term demon appears in several thought experiments: Maxwell's demon, Laplace's demon, Descartes' demon, maybe others.

What is this term supposed to mean?

For example, I understand the term oracle: an oracle is a black box that, for specific questions, always returns the right answer. For example, you can't have a turing machine for the halting problem, but you can talk about what you could do with an oracle for the halting problem.

But what about demon? What is the common characteristic that makes a thought-experiment entity a "demon"?

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    It isn't a term. Each type of demon means exactly what the corresponding writer described it to do, they were not working from some common concept. To the extent that there is a common denominator, it is an imaginary being with some extra-human powers, specifically those needed in each specific scenario. More recent authors prefer to use some imaginary "machines" instead, e.g. Nozick's experience machine. Sign of the changing times.
    – Conifold
    Commented Aug 3, 2020 at 7:42
  • 20
    More like common demoninator, ammiright? Sigh. Yes I joined just to make that lame joke. You can ban me now mods.
    – stib
    Commented Aug 4, 2020 at 2:36
  • Note that Descartes’ demon was originally described (in French) as mauvais génie, and (in Latin) as genium malignum. The word in both cases is not exactly a demon, but is a the Roman notion of a genius, a kind of divine spirit inhabiting every kind of thing. (The word is the source of the English word “genius”, but, oddly, is not related to the kind of genie that comes out of a magic lamp.) Commented Aug 5, 2020 at 5:27

7 Answers 7


A demon is a skilled entity, used in thought experiments, that remarks some fact. See https://en.wikipedia.org/wiki/Demon_(thought_experiment).

  • 3
    I'm not sure how a question that is answered by a single sentence and a link to wikipedia remains unclosed-as-trivial
    – CGCampbell
    Commented Aug 4, 2020 at 0:14
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    @CGCampbell It may survive on the basis of providing a superb response in a manner that Occam would be impressed by. Commented Aug 4, 2020 at 12:33
  • @CGCampbell When you gamify philosophy, philosophy becomes a game.
    – user4894
    Commented Aug 4, 2020 at 21:46
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    It's not clear what "remark" is supposed to mean here. Commented Aug 5, 2020 at 21:00

Consider Descartes

I will suppose therefore that not God, who is supremely good and the source of truth, but rather some malicious demon [mauvais génie] of the utmost power and cunning has employed all his energies in order to deceive me.

Vs Nozick

Suppose there was an experience machine that would give you any experience you desired. Super-duper neuropsychologists could stimulate your brain so that you would think and feel you were writing a great novel, or making a friend, or reading an interesting book. All the time you would be floating in a tank, with electrodes attached to your brain.

Almost every culture and era has described things we might call demons in different ways. A much less fixed line between metaphor, personification, natural process and conscious entity, was drawn in the past.

Philosophically they are pretty much black boxes which can perform whatever function the thought-experiment needs, but adds some drama.

It is perhaps worth noting Maxwell did not use the term demon, but that has become the universal way to refer to his idea

In his letters and books, Maxwell described the agent opening the door between the chambers as a "finite being". William Thomson (Lord Kelvin) was the first to use the word "demon" for Maxwell's concept, in the journal Nature in 1874, and implied that he intended the mediating, rather than malevolent, connotation of the word. - Wikipedia

Superdeterminism seems to me a modern version of Laplace's demon.

Maxwell's demon and Laplace's demon, are both substantially dispelled by understanding the physical reality of information.

  • In the specific case of Maxwell's demon, this was some magic entity that could perform some miraculous task that was physically impossible, which was invented as part of a thought experiment in the field of thermodynamics. Specifically, it could separate fast-moving molecules of gas from slow-moving ones and thereby build up reservoirs of cold and hot bodies of gas without performing any work. Those hot and cold sinks could then be used to power a heat engine, which would produce useful work out of nothing. Commented Mar 9, 2021 at 0:50
  • @nielsnielsen: was there something in my post that made you think I didn't know that?
    – CriglCragl
    Commented Mar 9, 2021 at 19:42
  • you have lost me here, what are you getting at? Commented Mar 10, 2021 at 3:53

A demon in these contexts refers to "a forceful or skilful performer of a specified activity." In these thought experiments, a demon performs a task exactly as intended.

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    I think it's worth noting here that this is also why computing adopted the term daemon as a process that runs continuously in the background performing a specific task without user interaction. In fact, according to one of the people that worked on Project MAC at MIT, the name "daemon" was inspired specifically by Maxwell's demon: takeourword.com/TOW146/page4.html
    – Bloodgain
    Commented Aug 5, 2020 at 18:59

It all depends on what society is asking

If religious, then: Supernatural being

A Demon is a supernatural being, typically associated with evil, prevalent historically in religion, occultism, literature, fiction, mythology, and folklore; Demon

However if one is a member of a philisophical society, a Demon may be more of a Cartesian doubt.

Cartasian doubt

Cartesian doubt is a systematic process of being skeptical about (or doubting) the truth of one's beliefs, which has become a characteristic method in philosophy.3 Cartasian doubt

So, your demons, are your doubts.

I cant do this: What says i am right?: Or your doubts could even be more serious than simply questioning if you have the ability to reach the summit of everest. Perhaps one could be doubting the nature of reality!

The Evil Demon

Descartes reasoned that our very own experience may very well be controlled by an evil demon of sorts.[12] This demon is as clever and deceitful as he is powerful. He could have created a superficial world that we may think we live in.1 As a result of this doubt, sometimes termed the Malicious Demon Hypothesis, Descartes found that he was unable to trust even the simplest of his perceptions. The evil demon


Perhaps we can start with the earliest use in philosophy: Socrates's "daemon," which is described as an "inner voice," of judgement--benign, not malevolent. For the Greeks the term usually meant an intellgent being above men, but below the gods.

So it is from the beginning a piece of unspecified intelligence capable of some minimal judgment and of acting in the world. For Socrates, it was said to prevent him from some unwise or unjust action. For Maxwell, this judgement is again a kind of minimal prevention, the operation of his little thermodynamic trapdoor sorting out molecules into two types.

The uses by Descartes and Laplace are in some ways very different. Descartes' demon is not only malevolent, but anthropomorphic, willful, and multitalented. Laplace's demon is both supremely "intelligent" and mechanical, no mention of judgments or intentions.

So the term seems pretty informal. If the Greeks placed the daemon between men and gods, we might today place it between men and machines. It has some aspects of judgment and will, accountable neither to human will nor to mechanical causation. In which case, Laplace's demon, both godlike and mechanical, seems like the odd one out.


Socrates said he had a daemon. This is probably an allusion to divine inspiration which he noted in the Phaedrus as the highest form of poetic inspiration.

With the advent of Christianity, the daemons of paganism became the demonic powers of the supernatural.

Why Maxwell decided on calling his supernatural power a demon rather than an angel is lost to history. Perhaps he was merely referring to Descartes demon. And its easy to see why Descartes called it a demon, he supposed it to be trying its utmost to deceive him - which is typically demonic and Machiavellian.


In greece "demon" is close to δαιμόνιον i guess. δαιμόνιον was belong to god power. δαιμόνιον is an art of prediction(Xenophon).

Demon(in middle times) is the concept of trying to control/manipulate some outside power and the ability to predict the following events of his behavior. Demon must be an evil, obliviously because the predictor of the demon's control is self good intention the demon owner. You don't have to control something good, but you have to control something evil.

Daemon ex machina was the trying of natural philosophy(magic) view at the creation of the reality, but it was replaced more utilitarian theory of games and probability theory - you can't control the demon, but you can play with him with the probability to win. But you need to draw up a contract (game rules/algorithms) with the demon/evil/devil... Contract may to play with evil but not to be the owner of the evil, and you intentions not may be good only, your intentions are hidden. You always can say: "it is not my evil I had a contract rules", or "I played with evil but i m not an evil", and same.

But DEM is a magic view on the things in synthetic world. Simplified daemon ex machina it is mechanical and physical tools with "the spirit of the god inside"(energy) - the clock, the bulb...

Today the idea of the DEM concept is steal alive but in modern variant - the smartphone is a typical daemon ex machina in a thing realization. Tool with smart ability or the smart desine of management the user behavior - gadget.

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