Difference Between Hallucinations and Illusions

The object causing the hallucination does not exist in objective reality, while the object causing an illusion does have a corporeal existence. The cognitive, auditory, visual and tactile senses of the individual misinterpret the external stimuli of the real object- effectively producing illusions.


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Both these kinds of episodes are commonly experienced by people, although hallucinations are often classified as symptoms of psychological ailments.

Hallucinations vs Illusions

The difference between hallucinations and illusions is that while hallucinations occur in the absence of any real external stimuli, illusions are episodes produced as a result of a mismatch between the external stimuli and its perception by the individual.

Hallucinations vs Illusions

Comparison Table

Parameters of ComparisonHallucinationsIllusions
DefinitionThey are states produced by false perceptions of internal stimuli.They are states produced by misinterpretation of real stimuli.
StimuliThe stimuli that initiate the episode are not real.The stimuli that initiate the episode are real.
Universality of the ExperienceHallucinations are extremely personal and cannot be universally uniform. They cannot be shared experiences.Illusions can be experienced simultaneously and uniformly by a group of people. They can be engineered as shared experiences.
Connotation of the EpisodeHallucinations are considered to be abnormal and associated with a pathological state of the mind.Illusions are considered to be fairly common to be experienced by a healthy, normal individual.
Use for Mental StimulationHallucinations are not used for active mental stimulations.Illusions are commonly used for mental stimulation through works of art and architecture

What are Hallucinations?

Hallucinations are caused by the perception of objects that do not exist. Originating from the Greek word ‘hallucinat’, they are defined as false perceptions caused by malfunctioning of the central nervous system.

They may present as symptoms of psychosis in an individual. Hallucinations are often associated with diseases like Schizophrenia, Parkinson’s and Post-Traumatic Stress Disorder.

Such psychosensory disruptions can be both auditory as well as visual episodes. These experiences may often be defined as ‘voices’ by the individual experiencing them.

Olfactory and somatic hallucinations are also common. The former refers to smelling something that is not present in the corporal world and the latter refers to a feeling that one’s body is being injured.

An individual may feel his skin crawling as part of a hallucinatory episode or he may see patterns or objects where there are none. Three essential grounds that have to be satisfied for an episode to be classified as a hallucination.

These conditions are: the object of the episode has to be unreal; the episode has to produce a sensory experience; and finally, the individual experiencing the hallucination has to be convinced of its contextual reality.


What are Illusions?

Illusions are misinterpreted perceptions. The stimuli or objects of such perceptions are real, but their interpretation is flawed.

Illusions are produced when our sensory organs misinterpreting external stimuli. These episodes may be classified into different categories of visual, olfactory, cognitive, optical and geometric illusions.

Psychologists have studied illusions to understand the operation of the human perceptive system. The perception of certain events in an erroneous manner can lead to the development of illusions.

Overstimulation of sensory organs may also result in illusions. When a discrepancy occurs between the varieties of information relayed through our multiple sensory organs, illusionary episodes are commonly experienced.

Here the facts of corporeality are being misinterpreted by our cognitive system.

For instance, a child experiences an illusion when she interprets the shadows in the dark as monsters or animals. This is an apt example of an illusion caused by the improper interpretation of visual cues.


Main Differences Between Hallucinations and Illusions

  1. The main difference between hallucinations and illusions is in terms of perception. False perceptions with no corresponding external stimuli result in hallucinations. Illusions are produced due to an erroneous perception of very real, existent stimuli. They are often called ‘sensorial errors’.
  2. The second difference can be stated in terms of the corporeal existence of the stimuli that produce each kind of episode. While hallucinations are the result of non-existent stimuli, illusions are episodes created by real stimuli. Moreover, in the former, the perceived stimuli are internal, while for the latter the stimuli are always external.
  3. Illusions can be shared experiences, while hallucinations are more commonly intimate and personal. For instance, optical illusions can be simultaneously experienced by all audience members at a magic show. As hallucinations are produced by internal stimuli, they tend to be specific to the individual and his prior experiences and mindset.
  4. The experience of illusions is considered to be quite normal in individuals, however, hallucinations can be symptomatic expressions of psychological ailments like Schizophrenia and Dementia.
  5. Optical illusions are easier to be researched and theorized effectively. Hallucinations are deeply personal experiences, as a result, the possibility of researching these experiences is minimal and extremely strenuous.
  6. Illusions are considered to be ways of stimulating the mind. Optical illusions are often reflected through works of art to encapsulate and interest the audience. Magicians also use optical illusions to allure the interest of their audience members. However, hallucinations are not used for positive mental stimulations. Their occurrence- if not induced medically or by a substance – often is linked to psychiatric pathology. They are produced by internal stimuli that are so personal and specific to individuals- unlike illusions- that it is impossible to induce them in large populations.
Difference Between Hallucinations and Illusions


  1. https://ajp.psychiatryonline.org/doi/pdf/10.1176/ajp.58.3.443
  2. https://www.ncbi.nlm.nih.gov/pubmed/10420378
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