Concept
Illusion
Overview
An illusion is a distortion of the senses, which can reveal how the mind normally organizes and interprets sensory stimulation. Although illusions distort the human perception of reality, they are generally shared by most people.
Illusions may occur with any of the human senses, but visual illusions (optical illusions) are the best-known and understood. The emphasis on visual illusions occurs because vision often dominates the other senses. For example, individuals watching a ventriloquist will perceive the voice as coming from the dummy since they are able to see the dummy mouth the words.
Some illusions are based on general assumptions the brain makes during perception. These assumptions are made using organizational principles (e.g., Gestalt theory), an individual's capacity for depth perception and motion perception, and perceptual constancy. Other illusions occur due to biological sensory structures within the human body or conditions outside the body within one's physical environment.
The term illusion refers to a specific form of sensory distortion. Unlike a hallucination, which is a distortion in the absence of a stimulus, an illusion describes a misinterpretation of a true sensation. For example, hearing voices regardless of the environment would be a hallucination, whereas hearing voices in the sound of running water (or another auditory source) would be an illusion. So, it should not be wrong to consider that illusions are just "misinterpretations" of how our brain perceives something that exists (unlike a hallucination where a stimulus is absent).
Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).
In the original texts
Passages from public-domain books where Illusion is discussed.
When I say that they are illusions, I must define the meaning of the word. An illusion is not the same as an error, it is indeed not necessarily an error. Aristotle’s belief that vermin are evolved out of dung, to which ignorant people still cling, was an error; so was the belief of a former generation of doctors that _tabes dorsalis_ was the result of sexual excess.
Sigmund Freud, The future of an illusion
names the idea; states what it is; the book is about it; opens on it
These three specimens of illusion are on the whole designed only for the more nobly endowed natures, who in general feel profoundly the weight and burden of existence, and must be deluded into forgetfulness of their displeasure by exquisite stimulants. All that we call culture is made up of these stimulants; and, according to the proportion of the ingredients, we have either a specially _Socratic_ or _artistic_ or…
Friedrich Wilhelm Nietzsche, The Birth of Tragedy
states what it is; names the idea; opens on it
But precisely this illusion is her misfortune. It is not seldom the case that nature comes to the assistance of an afflicted creature by consoling him with the notion that he is the most beautiful.
Søren Kierkegaard, Selections from the Writings of Kierkegaard
names the idea; states what it is
Therefore Nature attains her ends by implanting in the individual a certain illusion by which something which is in reality advantageous to the species alone seems to be advantageous to himself; consequently he serves the latter while he imagines he is serving himself. In this process he is carried away by a mere chimera, which floats before him and vanishes again immediately, and as a motive takes the place of…
Arthur Schopenhauer, Essays of Schopenhauer
states what it is; names the idea; opens on it
The other illusion is near akin to the first. It has the same origin, being also due to the fact that we import into speculation a procedure made for practice.
Henri Bergson, Creative Evolution
states what it is; names the idea; opens on it
Philosophers who discussed Illusion
Related ideas
Place in the tradition
Part of Acosmism.