Quadratic Equation

The Ancient Greeks seemed to believe that just about everything was made out of four of something else.

For instance, the physical world was thought to be composed of earth, wind, water, and fire; for the human body the four humours were blood, black bile, yellow bile, and phlegm.

Tidy model. What are an identitifier's 'humours'? How about linkability, discoverability, uniquenessability, and memorability?

In On the Nature of Man, Hippocrates wrote that

health is primarily that state in which the constituent elements [the four humours] are in correct proportion to each other, both in strength and quality, and are well mixed. Pain occurs when one of the substances presents either a deficiency or excess.

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Could have been a consultant. Or a therapist.