In 1847, George Boole, an English mathematician, defined a new type of algebra that could adopt only two values, true or false. These values are named as 0 and 1. These symbols do not represent numbers but two different type states within a device, such as switched on or off, opened or closed and so on. 

A logic variable is a variable which can only have two possible values, so that one value excludes another, i.e. if you have a value you cannot have another one. For example, YES or NOT or also 0 or 1. Let's imagine that A is a variable that stores the answer to a question. Is the bulb switched on? It can only have two answers: yes or no. If it is YES, it cannot be NOT, if it is NOT it cannot be YES. Normally, the logic variables are represented by 0 or 1 in number form, which conforms the number binary system used in digital systems (within the digital systems the computational ones are included).

Combinations of logic variables in sentences such as: something will be true when "A" is true or 1 and "B" will be true or false, allows us to state that a logic function is created. The previous statement can be expressed in Boolean terms as S = A·B.