A philosophy beyond the limits of rationality

According to Stephen Toulmin, a professor at the University of Southern California, there are signs all around us, from medicine to economics, that modern science needs an infusion of common sense.

As Toulmin shows in this readable and fascinating account, the practice of reason that produced modern science goes back to the 17th century, when traditional reasonableness was replaced by the model of geometry. As the goal of reason, likelihood was replaced by certainty; nature, including human nature, was replaced by Newton's nature, predictable and self-consistent.

Eventually - and this is perhaps one of Toulmin's most challenging insights - what came of this change is the system of disciplines that govern modern intellectual life. And so research universities may resemble madhouses, each researcher locked in his dream of reason, incapable of addressing the needs of others or of society at large.

For instance, when a doctor delivers the results of the diagnosis - "There's nothing we can do" - he all too often washes his hands of the patient. Indeed, young doctors "still tend to see the first patient they 'lose' as a total failure; it takes more mature physicians to see that the manner of a patient's dying is not less a mark of success or failure than the fact of his or her death."

This book is a call for "reflective practitioners," people more willing to be "reasonable" than strictly "rational." Toulmin bases his concept of reasonableness on the model of "knack," the instinctive knowledge that cooks and musicians and baseball players exhibit as they go about their jobs. While modern reason is expressed by strings of logic and statistical columns, knack is rooted in non-verbal knowledge.

The ancients understood knack. Toulmin cites the cunning Odysseus, whom Homer understood to be invested with this pre-scientific wisdom; he also cites the Chinese sage Chuang Tzu, who imagines a cook whose dimensionless blade separates bone from meat effortlessly, for the cook "tries to use what cannot be measured in an entirely practical way." Anyone dealing with real-life problems knows the value of Chuang Tzu's chopper.

As a teacher of writing, I long ago lamented that the geometrical model rules in the "rules" by which we instruct students to express their opinions. They follow the geometric method of proof. The appearance of certainty is what counts. No attempt is made to actually test the validity of the thesis against real cases; nor are students rewarded if they change their minds and actually learn something in the process of writing an essay. But clearly, composition should be the practice, not of abstract reason, but of what Toulmin calls reasonableness.

Testing his own theory from a wide assortment of cases drawn from history - from Homer to Nazi propaganda movies, from Euclid to modern economics - Toulmin defends and exemplifies the practice of reasonableness. There are passages when Toulmin's argument begins to drift, but that is the vice side of the virtue he is defining and defending - the virtue of reasonableness.

Throughout "Return to Reason," Toulmin calmly addresses complex situations arising in modern disciplines. Indeed, the knack he shows for reasonableness illustrates his thesis. His book is both a diagnosis and, by example, a cure for what ails our scientific culture.

Thomas D'Evelyn is an editorial consultant in Providence, R.I.