Logic in Forensic Science


49 Pages Posted: 11 Jun 2009 Last revised: 29 Jun 2009

See all articles by Ruggero J. Aldisert

Ruggero J. Aldisert

United States Court of Appeals for the Third Circuit

Date Written: 2006


Forensic science in the courtrooms and public safety organizations is generally considered a modern phenomenon, with the development of the great profession of forensic pathology and the availability of university-trained criminalists, crime scene specialists, toxicologists and laboratory PhDs. And, to be sure, forensic scientists are now the most popular heroes of current television, if you look at the skyrocketing ratings of shows like Law and Order and the CSI franchise. But the first popular forensic scientist appeared over 100 years ago when Sherlock Holmes arrived on the scene in 1901. In the first novel, A Study in Scarlet, when Dr. Watson was looking for a man to share lodgings, a friend referred him to Holmes, who was then working in the chemical laboratory of a hospital. The friend said, “I believe he is well up in anatomy, and he is a first class chemist; but, as far as I know, he has never taken any systematic medical classes.” Watson later tells us that “[s]ometimes, [Holmes] spent his day at the chemical laboratory, sometimes in the dissecting rooms . . . and [he] has a good practical knowledge of British law.” That’s a pretty good resumé for any forensic specialist.

But essentially he has been referred to as “Holmes the Deductive Machine.” And the success of all the stories came from “the aptitude of Holmes’ deductions drawn from clues which, with scrupulous fairness, are always laid before the reader.” With Holmes as a backdrop I have several theses I intend to defend in these pages:

• A professional in forensic science can use logic and still be wrong. • But a professional who does not use logic can never be right. • Most professionals in forensic sciences use deductive and inductive reasoning every day without realizing they are applying the canons of logic.

Some who master the technique of reasoning are not always certain what it is. Certainly, they learn how to do it, some of it. They pick up idiosyncratic signals somewhere and even a playbook. They learn how to go through the process, and occasionally, they learn why they do it. Others do not know exactly what is being done. They learn the exercise. They go through the motions. But most are a little shy on theory. This chapter is a modest attempt to fill that void. It is directed to “the what” of formal reasoning, or, if you will, logic, a term I use interchangeably with reasoning. Our purpose here is to explain, in very broad strokes, the basics of logic and its application to your profession, to describe the mental processes we utilize in reflective thinking. The purpose, quite frankly, is to get you thinking about thinking; or to suggest that if using reflective thinking was good enough for Sherlock Holmes, it should be good enough for you. It is also a plea to avoid making conclusions on the basis of hunch or intuition. Judge Joseph C. Hutcheson of the U.S. Court of Appeals for the Fifth Circuit was fond of saying that decisions may emerge from four separate processes: “first the cogitative, of and by reflection and logomachy; second, aleatory, of and by the dice; third intuitive, of and by feeling or ‘hunching;’ and fourth, asinine, of and by an ass.” Whatever decision making technique you may choose to make in your personal life, when it comes to the legal profession, you have one option only – reflective thinking.

Author copyright retained; posted with permission of the book editors.

Keywords: logic, forensics, forensic science, law, Aldisert

Suggested Citation

Aldisert, Ruggero J., Logic in Forensic Science (2006). FORENSIC SCIENCE AND LAW: APPLICATIONS IN CIVIL, CRIMINAL AND FAMILY JUSTICE, Chapter 2, Cyril H. Wecht & John T. Rago, eds., 2006, Available at SSRN: https://ssrn.com/abstract=1416233

Ruggero J. Aldisert (Contact Author)

United States Court of Appeals for the Third Circuit ( email )

601 Market Street
Philadelphia, PA
United States

Here is the Coronavirus
related research on SSRN

Paper statistics

Abstract Views
PlumX Metrics