In philosophy, reason is the ability of the human mind to form and operate upon concepts in abstraction, in accordance with rationality and logic —terms with which reason shares heritage. Reason, like consciousness with which it is also intimately connected, has traditionally been claimed as distinctly human, and not to be found elsewhere in the animal world. However, recent studies in this area show that, in lower levels, animals are capable of some types of thinking similar to that of humans. Discussion and debate about the nature, limits and causes of reason could almost be said to define the main lines of historical philosophical discussion and debate. Discussion about reason especially concerns:

* its relationship to several other related concepts: language, logic, consciousness etc,
* its ability to help people decide what is true, and
* its origin.

Also see practical reason and speculative reason.

The concept of reason is connected to the concept of language, as reflected in the meanings of the Greek word "logos", later to be translated by Latin "ratio" and then French "raison", from which the English word derived. As reason, rationality, and logic are all associated with the ability of the human mind to predict effects as based upon presumed causes, the word "reason" also denotes a ground or basis for a particular argument, and hence is used synonymously with the word "cause."

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