Illusion

In psychiatric terminology an illusion occurs when we misinterpret some data from the senses. Illusions are what happen when we look at magic shows, or optical illusions. It is different to a hallucination, where the initial sensory input is itself corrupted, here it is the mind's interpretation of sense data that is wrong. That's the official line anyway, frankly I am skeptical that enough work has been done with people's skulls open to define hallucination like that. How do we know whether the error arises in the sensory apparatus or during interpretation in the brain ?

Il*lu"sion (?), n. [F. illusion, L. illusio, fr. illudere, illusum, to illude. See Illude.]

1.

An unreal image presented to the bodily or mental vision; a deceptive appearance; a false show; mockery; hallucination.

To cheat the eye with blear illusions. Milton.

2.

Hence: Anything agreeably fascinating and charning; enchantment; witchery; glamour.

Ye soft illusions, dear deceits, arise! Pope.

3. Physiol.

A sensation originated by some external object, but so modified as in any way to lead to an erroneous perception; as when the rolling of a wagon is mistaken for thunder.

⇒ Some modern writers distinguish between an illusion and hallucination, regarding the former as originating with some external object, and the latter as having no objective occasion whatever.

4.

A plain, delicate lace, usually of silk, used for veils, scarfs, dresses, etc.

Syn. -- Delusion; mockery; deception; chimera; fallacy. See Delusion. Illusion, Delusion. Illusion refers particularly to errors of the sense; delusion to false hopes or deceptions of the mind. An optical deception is an illusion; a false opinion is a delusion.

E. Edwards.

© Webster 1913.