In the 1670s, Dutch draper Anton van Leeuwenhoek indulged in his hobby of painstakingly grinding little lenses, which he used to magnify everyday objects, such as ditch water. He then sketched what he saw. In 1677, van Leeuwenhoek discovered small living creatures, too small to see without magnification, swimming about in ditch water. And in 1683, he caught his first glimpse of the even smaller objects that we call bacteria. (Isaac Asimov, Past, Present, and Future (New York: Barnes and Noble, 1987), p. 80)
From the perspective of three centuries after Leeuwenhoek lived, his discovery of microscopic life forms was obviously of significant practical value. In the 1860s, French scientist Louis Pasteur demonstrated that microorganisms cause infectious disease. That, in turn, enabled the medical profession to make dramatic advances, curing more disease than they caused, raising life expectancy from thirty-five to seventy or more years.
Yet, practical wisdom is not synonymous with prudence, the second of the four cardinal virtues. The Greek word phronesis became prudence in Latin. Prudence "consists of the capacity, the aptitude, for discerning the right rule, the orthos logos, in difficult situations requiring action." (Paul Ricoeur, Reflections on the Just, trans. D. Pellauer (Chicago: University of Chicago Press, 2007), p. 54)
In sum, the virtue of prudence denotes a subset of practical wisdom, that is, the wisdom to recognize and classify a moral challenge, to discern the moral issues involved, and to develop an appropriate response to that challenge. Plato, in contrast to Aristotle's spotlight on courage, taught that prudence is the chief virtue.
Neither the discovery of microscopic organisms or of their role in causing disease is an example of prudential wisdom, though both discoveries have had tremendous beneficial effects on the quality and length of human life. Instead, the willingness (or unwillingness) of medical practitioners to adopt procedures and protocols informed by those discoveries exemplifies prudential wisdom: recognizing a moral challenge, discerning the issues involved, and developing an appropriate response to the challenge.
Candice Millard's The Destiny of the Republic (New York: Random House, 2011) tells the story of U.S. President James Garfield's assassination through four interlocking stories: that of Garfield, his assassin Charles Guiteau, Joseph Lister, and Alexander Graham Bell. When Guiteau shot Garfield in the back in 1881 at Union Station in Washington, D.C., the wound was not fatal. The wound became infected when multiple doctors stuck their fingers and non-sterilized instruments into the wound, searching for the bullet. In time, the infection would kill Garfield.
Garfield's primary physician had attended an 1876 lecture at the Philadelphia Centennial Exposition by Lister, the leading medical proponent of sterilization, building on work by Leeuwenhoek and Pasteur. Yet the physician scoffed, blinded by ego fueled by previous errors as an early adopter of an unproven new technology. The physician lacked the prudential wisdom to recognize a moral challenge (how best to care for the patient), the moral issues involved (an insistence on his status and prerogatives as a physician trumped patient welfare), and consequently refused to sterilize his equipment, his clothes, or his person. Prudence would have had the physician maintain an open mind, examine the data (e.g., look through a lens to see microscopic organisms on his instruments and compare Lister's surgical results with his own), and then make an appropriate choice.
The physician's ego needs drove him to keep much of his treatment of Garfield a secret. Thus, he did not disclose to Bell, who had invented an instrument that detected anomalies in a magnetic field as a way to locate a bullet in the body, that Garfield's mattress rested on a metal frame. Bell had worked feverishly to perfect the device when doctors could not locate the bullet in Garfield's back in spite of repeated attempts.
Once again, the physician lacked prudential wisdom, failing to prioritize patient well-being in accordance with the Hippocratic Oath, blinded to the real issues by his emotional needs and professional aspirations, and then making bad choices.
At what points in your life do your ego, emotional needs, past mistakes, or professional aspirations cause you to fail to recognize moral challenges, discern the issues involved, and then to make poor choices?