Presocratic Greek philosopher Heraclitus [Herra-cl-eye-tus] gave us the following fragment to consider:
Sea water is very pure and very foul, for, while to fishes it is drinkable and healthful, to men it is hurtful and unfit to drink.
What I want to draw from this fragment is that purity or foulness is not a property of the water, but a reaction of the individual towards the water.
This relates to a discussion of the definition of health and disease in the philosophy of medicine. Philosophers of medicine have invested a great deal into trying to define what disease is. Is blindness a disease, for instance. Heraclitus looked at the difference in reaction between a man and a fish. I want to extend this to looking at the difference between individual human beings.
Sea water is foul to a man because he is not biologically adjusted to it, whereas a fish is adjusted to it. In the same way, a man born blind may be perfectly well adjusted to life without sight and ought not be labelled as diseased, but a man who has had sight all his life and is blinded as the result of an accident may be called diseased since he is maladjusted to his new condition and may be wise to seek treatment.
So where philosophers of medicine have troubled to seek a definition of disease to suit all of mankind, I counsel against being so general.
I instead seek a kind of meta-definition that would compare a man's actual condition with the condition that he is adjusted to.
I am interested in looking at an individual's biological fitness and how it fluctuates on a local basis. I am examining a definition of disease that focuses on an individual's fitness reaching a certain threshold below his local average as the result of a certain event or culmination of circumstances.
The individual in the graph below is considered diseased after the time his fitness dips below the disease threshold.