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), $\lor$ (or), $\neg$ ([negation), and $\to$ (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.