In English the word reason has long had, and still has, a large number and a wide variety of senses and uses, related to one another in ways that are often complicated and often not clear. However, there is one particular sense of the word in which it, with its synonyms or analogues in other languages, has figured prominently in philosophical controversy. This is the sense, sometimes distinguished typographically by an initial capital, in which the term is taken to designate a mental faculty or capacity—in which reason might, for example, be regarded as coordinate with, but distinguishable from, sensation, emotion, or will.

Questions to Be Examined

The question that has been chiefly debated by philosophers might be expressed succinctly, but far from clearly, as "What can reason do?" However, there has also been discussion of the question whether the faculty of reason is peculiar to humanity...