Etymology and culture notes for class 3 --------------------------------------- "Boolean" is named for George Boole, a mathematician who wrote the influential book _An Investigation into the Laws of Thought, on Which are Founded the Mathematical Theories of Logic and Probabilities_ (usually called _The Laws of Thought_). Boole was one of the pioneers of modern mathematical logic. In modern use, "Boolean" refers to something which can have two values, conventionally called "true" and "false", or "1" and "0". So a Boolean variable is a variable which can have either a true value or a false value. Likewise, a Boolean expression is an expression which has either a true value or a false value. A Boolean operator is an operation which takes several Boolean variables and produces a single Boolean result. Boolean algebra is the notation devised by Boole -- which has now been modernized somewhat -- for writing and reasoning about Boolean expressions. It has similarities to and differences from the algebra you may be used to, and there are many useful theorems in Boolean algebra, such as De Morgan's law. The fundamental association of Boolean algebra to computers was made by the great mathematician Claude Elwood Shannon (1916-2001), who wrote "A Symbolic Analysis of Relay and Switching Circuits", which explained how computer circuits could be analyzed in terms of Boolean algebra. Today, all computer engineers and most electronics engineers use Boolean algebra to describe the circuits they implement.