The word “irrational” (as used in context to philosophy and science) derives from the Latin irrational, meaning “beings not applicable to human reason.” Thus, irrationalism is a pessimistic philosophical viewpoint that holds that the attempts of mankind to find a rational explanation or meaning in the universe generally fail (and, therefore, are irrational), as no such rational explanation actually exists. Philosophers who support this view include Immanuel Kant, Leo Tolstoy, Bertrand Russell, John Locke, and Albert Einstein. According to the majority of philosophers, only God can provide an explanation for the existence of the world and life on earth, and man can only deduce significance from the existent facts.
In contrast, many people who believe in the reality of God and the existence of an unactualized God or divine reality view absurdism as the true philosophy of religion. They maintain that absolute irrationality is tantamount to evil, while religious believers are merely mistaken in their belief that God speaks through words or actions. While both absurdism and religion have their critics, most agree that it is important to recognize the difference between the two philosophies. They further argue that the source of differences lies in the fundamental arguments of both philosophy – that reality is inherently irrational and that God is capable of speaking – and that a person cannot be confused between the existence of God and the irrationality of religious beliefs.
Philosophers who believe in absolute irrationality point out that there are many examples of how this occurs, including Descartes’ view that all ideas are merely accidents. However, some existentialists point out that there are a number of truly absurd ideas, including concepts that derive from mathematics and science (e.g., objectivity, certainty, and consistency) as well as those that derive from human experience (e.g., the sense of smell, pain, and pleasure). In addition, some thinkers point out that absolute irrationality is not necessary to account for the existence of God, since God could not be irrational in order to exist. Moreover, other philosophers note that a God capable of communication with humans via faith would not need to be rational or absurd. Regardless of what you personally believe, it’s clear that you can’t easily dismiss Aquinas’ arguments against religion and ridiculousism without answering the question of what makes God a unique creature and thus a source of motivation for the existence of humans.