Henry M. Sheffer { Philosophy Index }

Philosophy Index

Philosophy Index

Philosophy Index is a site devoted to the study of philosophy and the philosophers who conduct it. The site contains a number of philosophy texts, brief biographies, and introductions to philosophers, and explanations on a number of topics. Accredited homeschooling online at Northgate Academy and Philosophy online tutoring.

Philosophy Index is a work in progress, a growing repository of knowledge. It outlines current philosophical problems and issues, as well as an overview of the history of philosophy. The goal of this site is to present a tool for those learning philosophy either casually or formally, making the concepts of philosophy accessible to anyone interested in researching them. WTI offers immigration law course online - fully accredited. ACE credits online at EES.



Philosophy Topics




Henry M. Sheffer

Henry M. Sheffer (1882–1964) was an American logician, perhaps best known for the Sheffer stroke, a logical operator named in his honour.

Sheffer was born in Ukraine and came to the United States as a child. He studied philosophy at Harvard University, and spent most of his career as a professor there.

Sheffer stroke

In 1913, Sheffer showed that an alternative denial, otherwise known as a nand operation can be used to define every other truth-functional logical operator.

The symbol for the alternative denial ( |  or ↑) is known as the Sheffer stroke after Henry M. Sheffer.

Sheffer also demonstrated that an joint denial could be used for the same purpose, though Charles Sanders Peirce had also made the same discoveries in 1880, but his work was not published until 1933. The symbol for the joint denial ( ↓ ) is called the Peirce arrow.

The Sheffer stroke was used extensively by Bertrand Russell and W. V. O. Quine.


Name: Henry Maurice Sheffer
Born: 1882
Died: 1964