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.
The role of reason
Until the 1970s, social scientists generally thought that peoples' actions were usually rational. This was challenged by a research in psychology that highlighted reproducible flaws in human judgement.  Errors may occur in cognition, and not just in logic, which results in incorrect choices, particularly in situations with incomplete information.
While intuitive thinking usually results in the correct or mostly correct answer, it sometimes is found to be misleading, such as in the cognitive reflection test which have intuitive answers which are incorrect. Many studies show the importance of intuitive thinking in decision making, with rational thought playing a complementary role.
- "In the picture that emerges from recent research, the intuitive System 1 [thinking] is more influential than your experience tells you, and it is the secret author of many of the choices and judgments you make. "
- Amos Tversky, Daniel Kahneman, Judgment under Uncertainty: Heuristics and Biases, Science, 1974
- Daniel Kahneman, Thinking, Fast And Slow, 2011