Chap X asked:

What is difference between reality and illusion?

Answer by Helier Robinson

Illusions are either contradictions between the senses, as in the half-immersed stick which is bent to the sight and straight to the touch, or between what is perceived and well established belief, as in the railway lines seeming to meet in the distance. A contradiction cannot be true, so illusions must be false perceptions and so unreal.

Reality has a number of definitions: it is all that we perceive around us which is not illusory; it is all that exists regardless of whether it is perceived or not; it is what makes statements true or false; and it is the genuine, as in real leather, real flowers, etc. These definitions are not necessarily equivalent, and careless use of them can lead to confusion through equivocation: for example, an argument I once heard was that illusions are real (genuine) illusions and therefore part of reality and so should not be distinguished from reality.

A further difficulty is that empirical objects are made up of sensations (colours, tactile sensations, etc.) and these exist only as long as they are perceived, so do not exist independently of being perceived, so are unreal. Philosophers have argued about such difficulties with perception throughout history. The almost universal view these days is that philosophy should conform to common sense, but this is a view that I deplore: philosophy exists just because of the inability of common sense to solve various problems.