Faith and rationality are two ideologies that exist in varying degrees of conflict or compatibility. Rationality is based on reason or facts. Faith is belief in inspiration, revelation, or authority. The word faith sometimes refers to a belief that is held with lack of reason or evidence, a belief that is held in spite of or against reason or evidence, or it can refer to belief based upon a degree of evidential warrant.
Although the words faith and belief are sometimes erroneously conflated and used as synonyms, faith properly refers to a particular type (or subset) of belief, as defined above.
Broadly speaking, there are two categories of views regarding the relationship between faith and rationality:
The Catholic Church also has taught that true faith and correct reason can and must work together, and, viewed properly, can never be in conflict with one another, as both have their origin in God, as stated in the Papal encyclical letter issued by Pope John Paul II, Fides et Ratio ("[On] Faith and Reason").
From at least the days of the Greek Philosophers, the relationship between faith and reason has been hotly debated. Plato argued that knowledge is simply memory of the eternal. Aristotle set down rules by which knowledge could be discovered by reason.
Rationalists point out that many people hold irrational beliefs, for many reasons. There may be evolutionary causes for irrational beliefs — irrational beliefs may increase our ability to survive and reproduce. Or, according to Pascal's Wager, it may be to our advantage to have faith, because faith may promise infinite rewards, while the rewards of reason are seen by many as finite. One more reason for irrational beliefs can perhaps be explained by operant conditioning. For example, in one study by B. F. Skinner in 1948, pigeons were awarded grain at regular time intervals regardless of their behaviour. The result was that each of pigeons developed their own idiosyncratic response which had become associated with the consequence of receiving grain.