Reasonism (similar to rationalism) is an epistemological theory that holds that reliance on reason is the best guide for belief and action. Philosophically, it is the theory that the exercise of reason, rather than experience, authority, or spiritual revelation, provides the primary basis for knowledge.
The term reasonist is used interchangeably with rationalist, both terms being used to distinguish them as true reasoners and rational inquirers.
A number of writers and thinkers have used the terms reasonist or reasonism to identify themselves or their philosophy respectively, often preferentially to the labels such as atheist or atheism. During the Beyond Belief Symposium (Enlightenment 2.0) in October 2007, UCLA historian Robert Winter explains to speaker Sam Harris that he refers to themselves (non-believers) as "reasonists", and others (religionists) as "areasonists", based on the historical fact that the prefix a- is always supplied by those who have the power within a given paradigm, to describe those who don't have that paradigm.