Reason involves the ability to think, understand and draw conclusions in an abstract way, as seen in human thinking. The meaning of the word "reason" overlaps to a large extent with "rationality" and the adjective of reason in philosophical contexts is normally "rational", not "reasonable".

In action, reasoning involves a conscious attempt to discover what is true and what is best. Reasoning thought follows a chain of cause and effect, and the word "reason" can be a synonym for "cause".

As one way of coming to conclusions, reason is often contrasted to emotion, tradition and faith - the "rationalist" argument being that reason is the more reliable way to arrive at that truth.

The concept of reason is closely related to the concepts of language and logic, as reflected in the multiple meanings of the Greek word "logos", the root of logic, which translated into Latin became "ratio" and then in French "raison", from which the English word "reason" was derived. In contrast to reason more generally, language refers not to the thinking as such, but to the communication or potential communication of rational thoughts.

Reason compared to logic, cause and effect thinking, and symbolic thinking

In modern times, there is an increasing tendency to use the terms logic and reason interchangeably in philosophical discussion, or to see logic as the most pure or the defining form of reason.

Reason and logic can be thought of as distinct, although logic is one important aspect of reason. Reason is a type of thought. Logic, as the word is used in modern languages, is the attempt to make explicit the rules by which reason operates. The oldest surviving writing to explicitly and at length consider the rules by which reason operates are the works of the Greek philosopher Aristotle, especially Prior Analysis and Posterior Analysis. Although the Ancient Greeks had no separate word for logic as distinct from language and reason, Aristotle's neologism "syllogism" (syllogismos) identified logic clearly for the first time as a distinct field of study. When Aristotle referred to "the logical" (hê logikê), he was referring more broadly to rational thought.

Author Douglas Hofstadter, in Gödel, Escher, Bach, characterizes the distinction in this way. Logic is what is done "inside the system" by formal steps such as deduction. Reason is what is done "outside the system" by such informal methods as skipping steps, working backward, drawing diagrams, looking at examples, or seeing what happens if you change the rules of the system.

Another way to consider the confusion between logic and reason is that computers and animals sometimes perform actions which are apparently logical: from a complex set of data, conclusions are achieved which are "logical". Being a cause of something which humans find logical does not necessarily mean that computers or animals have reason, or even logic in the strict sense. Some animals are also clearly capable of a type of "associative thinking" - even to the extent of associating causes and effects. A dog once kicked, can learn how to recognize the warning signs and avoid being kicked in the future. Human reason is something much more specific, requiring not just the possibility of associating perceptions of smoke, for example, with memories of fire, but also the ability to create and manipulate a system of symbols, or icons in the terminology of Charles Peirce, which have only a nominal connection to either smoke or fire.