Reason is the human faculty that allows one to draw valid (or at least useful) conclusions or inferences from given premises, assumptions or observations. It is closely related to logic and intelligence. A person who uses reason, or an argument based on reason, is described as rational; the opposite would be described as irrational.
There is much debate as to whether, or to what extent, non-human animals display reasoning abilities. The religious view is usually that only humans employ reason because it — along with consciousness, intelligence and language — is seen as a gift from God that sets humans apart from the (other) animals.
While reason is sometimes contrasted with faith ("belief without reason") as a method that can lead to truth, theology can be seen as the application of reason to questions about God. This can be problematic, however — especially when reasoning leads to answers that contradict scripture or established doctrine. Such contradictions often lead to schisms, or the splitting of one religious tradition into two or more different traditions.