Generally, the Missing Shade of Blue is an argument used by David Hume to convey his idea of sensory experience. He argued that it is impossible for the mind to create an idea or concept without being exposed to the rudiments of sensory experience. In short, perception precedes idea creation. In the latter part of his writings though, Hume seemed to contradict himself by offering a counter argument to his proposition/maxim. According to him, it is possible, at one instance, where the mind can generate idea without exposure to sensory experience.
Here is the situation. If an eye is presented with a set of predefined colours, then the eye (consequently, the person) will be able to distinguish the differences between those colours. What if then, if the person is blind, is it possible for him to create colours from combinations of colours presented to him? If the color blue was never presented to the person before he became blind, would it be possible for the person to create an idea of blue in his mind? Hume’s answer is yes.
Because of man’s ability to imagine preconceived ideas from general forms, a person (although with limitation) can generate a shade that was derived from two primary colours. Hume’s counter argument essentially altered the nature of his thesis. Note that if one assumes that ideas cannot be generated without impressions, then a possible negation of the proposition is not possible. This statement – ideas can be generated with impressions – is a negation of the earlier statement.
One is forced to admit that this new proposition allows a high degree of possibility. In analyzing Hume’s arguments, one should also differentiate logical possibility from practical possibility. His counter argument is logically possible but practically impossible (logical possibility – events that can occurred by positive deduction; practical possibility – actual occurrence of an event). As of today, psychologists fail to confirm Hume’s thesis.