In formal logic, a boolean variable is a variable that can take on one of only two possible values: “true” or “false”. Propositions can then be said to evaluate to one of these two values, in the same way that ordinary algebraic expressions evaluate to a number.
Also as in algebraic expressions, boolean values can be manipulated using certain operators such as (and), (or), ([negation), and (implication). This field is called, surprisingly, boolean_algebra.
Because booleans can only express absolute truth or falsity, when working with measures of uncertainty you must use other representations, such as probability.