Difference between illusion and hallucination

It is common for illusion to be used as a synonym for hallucination and vice versa, however, they are different concepts. The illusion is related to the misperception of a real stimulus while the hallucination is the perception of something that is not matched by any real physical stimulus.


It is the misperception or misinterpretation of a real external stimulus. For example, interpreting shadows as people or vegetation as animals. Many define an illusion as the result of a combination of poor clarity and an intense emotional state. The best known illusions are optical illusions and calves.

Anyone can experience illusions without this implying any disease. Some psychological disorders can cause pathological illusions, especially in people with psychosis.


A hallucination is nothing more than a perception that does not correspond to reality, however, whoever suffers from it feels it as real. A hallucination is usually considered as a pseudo-perception due to the absence of external stimuli. It is of interest to some sciences such as neurology, psychology and psychiatry.

It usually occurs in disorders such as schizophrenia, in some mystical and religious experiences and as part of drug use, sleep disorders and diseases such as cancer. Hallucinations are very common and can be caused by biological causes such as deficiencies in the normal functioning of the brain and by the proper functioning of our perception.

Differences between illusion and hallucination

  • Illusion is a phenomenon that arises when we perceive something real wrongly. That is, we perceive what is real as something that is not.
  • Illusions can be suffered by anyone without this implying that they are sick.
  • A hallucination is the perception of something without its presence in reality.
  • Hallucinations are very common and can have a biological cause or due to deficiencies in the functioning of the brain.

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