Research Article: Judgments of effort for magical violations of intuitive physics

Date Published: May 23, 2019

Publisher: Public Library of Science

Author(s): John McCoy, Tomer Ullman, Valerio Capraro.


People spend much of their time in imaginary worlds, and have beliefs about the events that are likely in those worlds, and the laws that govern them. Such beliefs are likely affected by people’s intuitive theories of the real world. In three studies, people judged the effort required to cast spells that cause physical violations. People ranked the actions of spells congruently with intuitive physics. For example, people judge that it requires more effort to conjure up a frog than to levitate it one foot off the ground. A second study manipulated the target and extent of the spells, and demonstrated with a continuous measure that people are sensitive to this manipulation even between participants. A pre-registered third study replicated the results of Study 2. These results suggest that people’s intuitive theories partly account for how they think about imaginary worlds.

Partial Text

Both children and adults spend much time engaged with make-believe worlds: children pretend, adults daydream, and both immerse themselves in movies and novels. But even in make-believe, not everything goes. Superman leaps tall buildings in a single bound, but a building takes more sweat than an ant-hill. And even for Superman, leaping to Alpha Centauri is simply silly.

In Study 1, participants showed a consistent ranking of spell difficulty, from changing color (easiest) to conjuring (hardest), and exposure to fantasy had no effect on how participants ranked the spells. Study 2 tests the effect of varying the target of each spell between participants while keeping the spell itself fixed (for example, levitating a frog vs. levitating a cow). Participants provided a continuous measure of spell difficulty, rather than giving rank judgments.

To heighten confidence in the results of the first two studies, we ran a third study with identical methods and stimuli as in Study 2, with pre-registered methods and analysis, and a larger sample size. Pre-registration details and materials can be found in an OSF repository at, under ‘registrations’.

Sadly, magic does not exist, but how do people think about worlds that have magic in them? More generally, how do people understand or construct imaginary worlds? We suggest that people draw on their intuitive theories of the real world to reason about imaginary worlds. In three studies, we presented people with spells that violated various physical principles and had them judge how much effort each spell required. Across the three studies, participants were consistent in how much effort they thought the different spells required. The target or extent of a spell (levitating 1 foot versus 100 feet) also affected how effortful a spell was judged. This is particularly striking given that participants saw only a single version of each spell. Exposure to fantasy or magic in the media had no effect on how much effort participants thought that different spells required.




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