Difference Between Illusion and Hallucination

Key Difference – Illusion vs Hallucination


Illusions and hallucinations are two terms that come up when we speak of perception. These, however, do not mean the same thing. In fact, there is a key difference between an illusion and a hallucination. An illusion is a misperception. Or in other words, it is when something appears to be something else. On the other hand, hallucinations refer to false perceptions. The key difference between illusion and a hallucination is that while an external stimulus exists in the case of an illusion, it does not exist in hallucinations. Through this article let us examine the differences between illusion and a hallucination in depth.

What is an Illusion?

An illusion refers to a misperception. This denotes an instance where the individual takes something for something else. In simpler terms, illusions distort the reality of objects. Illusions tend to deceive most people and are considered as normal. This is not restricted to a particular sensor organ although visual illusions are given prominence. It is important to highlight that other forms of illusions such as auditory illusions and tactile illusions also exist. In Gestalt psychology, attention is specifically paid to illusions that people can have. Gestalt psychologists point out various organizational principles that are significant when studying human perception and illusions.

What exactly counts as an illusion? For something to be an illusion, there must be an external stimulus. For an example, a branch of a tree can be perceived as an animal in the dark. This is a common mistake that we all tend to make. This can be categorized as a visual illusion. But hallucinations are very much different to illusions. Now let us look at hallucinations.

Difference Between Illusion and Hallucination

What is a Hallucination?

Hallucinations refer to false perceptions. The key characteristic is that in hallucinations there are no external stimuli. Hence, they can be the result of internal stimulation. Hallucinations are not universal as in the case of illusions. On the contrary, they tend to be unique and personal. In psychology, it is believed that people who are suffering from mental conditions experience hallucinations.

Let us take a small example. In the Shakespearean drama ‘Macbeth’, Macbeth begins to have hallucinations as the story progresses. He begins to see the ghost of Banquo. Here there are no external stimuli whatsoever. Hence, it can be considered as a hallucination that results from the guilty conscience of Macbeth. Even in day to day life, people can experience hallucinations. Having hallucinations is considered as one of the symptoms of schizophrenia, a mental disorder.

Key Difference - Illusion vs Hallucination

What is the difference between Illusion and Hallucination?

Definitions of Illusion and Hallucination:

Illusion: Illusion is a misperception.

Hallucination: Hallucinations refer to false perceptions.

Characteristics of Illusion and Hallucination:

External stimuli:

Illusion: In the case of an illusion, an external stimulus is present.

Hallucination: In hallucinations, an external stimulus is not present.


Illusion: Illusions are universal.

Hallucination: Hallucinations are not universal. They are personal.


Illusion: Normal people can also experience illusions.

Hallucination: Hallucinations are experienced by mentally deranged people.


Image Courtesy:

1. “Fraser spiral” by Mysid – Self-made in Inkscape; based on en:Image:Frasers.gif.. [Public Domain] via Commons

2. Tactile hallucination By Angela Mariam Thomas (Own work) [CC BY-SA 3.0], via Wikimedia Commons