The term reason comes from the latin ratĭo. The Larousse dictionary online provides many meanings for this word, among them the Faculty of thinking, the argument which is alleged to support a given thing, the reason or cause, and the quotient of two numbers.
For philosophy, the reason is the Faculty whereby the human being is able to identify concepts and put them into question. That said, happens to determine the consistency or the contradiction between them and can induce or infer others different from those that he knows already.
The reason involves several tautological principles (which are explained by themselves), such as the principle of identity (which highlights that a concept is same concept), the principle of non-contradiction (the same concept cannot be and not be at the same time) and the law of the excluded (between the fact of being or not being a concept where there is no "middle").
Furthermore, it is necessary to mention two major types of reasoning: deductive (which considers that the conclusion is implicit in the premises) and the inductive (it gets the General conclusions from a particular thing).
The reason of a geometric sequence is a constant coefficient in a comparison of two quantities by its quotient. It starts from the principle of the ability to determine how many times a contains the other.
Finally, it should be noted that there are numerous citations referring to the reason, namely, inter alia: «Raise the voice does not give reason» (Chinese proverb); "We love without reason and without reason it hates." "The heart has its reason that reason doesn't know point.