The Law of Parsimony, also known as Occam's razor, does not warrant a funeral but it does have some problems in its description of reality. This law states that the most simple of two competing theories should be the preferred one, and that entities should not be multiplied needlessly. It maintains a lofty stature in philosophy and science and is often utilized as a literary device. Using the Law of Parsimony is the essence of good detective fiction perhaps none better achieved than by Arthur Conan Doyle, a physician, who sharpened to perfection Occam's razor in the reasoning employed by his renowned creation, Sherlock Holmes. One of Holmes' most noted rules is that "when you have eliminated the impossible, whatever remains, however improbable, must be the truth."
As an absolute, the Law of Parsimony is floundering. Not because it is aging poorly, but rather because it is being challenged more and more by the complexity of the real world and its need for a valid counterweight. From my vantage point as a physician in the practice of clinical neurology, its usefulness, which has always been a guiding principle for me, can easily lead to blind spots and errors in judgment when rigidly followed.
A recent case in point is a 79 year- old woman who was complaining of difficulty with her balance with several recent falls. This could be dismissed to age. However, she has multiple other factors in her history that need to be taken into account including a diabetic neuropathy making her feet lose sensation as well as compression of her cervical spinal cord producing weakness in her legs. She also has a hearing problem with a long history of intermittent vertigo. In addition, she is of Scandinavian descent, making her somewhat more prone genetically to vitamin B12 deficiency secondary to poor absorption that in her case may be exacerbated by medications used to inhibit acid reflux. This vitamin deficiency by itself can produce neuropathy and degeneration of her spinal cord. It is in this complicated clinical setting that the Law of Parsimony utterly fails and I doubt that even the great Holmes, who has the luxury of being a fictional character, could tie all of these loose ends into a simple knot. To provide the appropriate care to this patient, I needed to utilize Hickam's Dictum, the medical profession's counterargument to Occam's razor. This maxim of Dr. John Hickam, who died in 1970, states very simply "a patient can have as many diagnoses as [she] damn well pleases."
The crucial role that the Law of Parsimony renders in how we reason is beyond question. This law dates back to the Greek philosophers who refined it from their antecedents since I suspect we evolved to seek simplicity over complexity. The desire for unity and singleness is satisfying and very seductive. However, at times it needs to be challenged by Hickam's Dictum, which is a variation of the Principle of Plenitude. This view of reality also dates to ancient Greek philosophy, which postulates that if the universe is to be as perfect as possible it must be as full as possible, in the sense that it contains as many kinds of things as it possibly could contain.
With the complexity, inconsistency, ambiguity and ultimate uncertainty that define our reality, we should not limit ourselves to using only one or the other of these valuable tools of analysis. We need to be more willing to have our own positions challenged, striving to keep an open mind to other arguments, other viewpoints and conflicting data. In order to make the best decisions for the best reasons, we must choose the appropriate heuristics coupled with intellectual honesty to guide our thinking as we grapple with the cunning machinations of the world we inhabit.