Reasonism is the general viewpoint and intellectual perspective of the West which began about 600 BC and which went into steep decline around 800 years later. It inaugurated Western Civilization and liberal culture. Reasonism slowly revived after 1300 AD and then started another precipitous decline 500 years later. As of 1985 or so reasonism has started to lightly ascend again. But what is it exactly?
Reasonism is the broad, general, philosophical belief that only the mind and thinking faculty can genuinely, reliably, and accurately discern the truth and the nature of the universe. It constitutes a family of related philosophies. In the mid-500s BC Pythagoras said: "Reason is immortal, all else mortal." About a century later another Greek, Sophocles, observed: "Reason is god's crowning gift to man."
Atomism, Aristotelianism, Epicureanism, Stoicism, and the very recent Objectivism are all reasonist thought-systems. Reasonism is the intellectual claim that only rationality can correctly, positively, and definitively determine neutral, objective, absolute reality. Reasonism is the argument that only reason leads to certain understanding and unquestionable knowledge.
Virtually all living animals of any development and sophistication—creatures of any complexity and subtlety—don't merely automatically and unthinkingly react to stimuli and their external environment. Rather, they respond based on mental activity and at least some version of rational calculation. The brain-led and organized central nervous systems of even insects and worms can be fairly said to "think." Highly self-conscious humans, naturally, think and need to think, with far more celerity and profundity.
Reasonism argues that mentally-volitional and free-willed human beings exist and process information in ways very different from lower-order animals. Even well-evolved mammals are largely mechanical and automatic in their "thinking" habits and techniques. Not so people. Humans have to truly work to focus and direct their minds. And they need to make such determined, vigorous, and intelligent choices in order to best survive and prosper.
Thus human beings should, in general, employ their minds as much as possible, aiming for great breadth, depth, and rapidity, as well as high accuracy. The theory of reasonism argues that all relatively intelligent creatures should try to be as reasonable, rational, logical, and scientific as possible—consonant with their fullest achievable pleasure, happiness, enjoyment of life, and fulfilling exploitation of that life. Higher-order beings should also attempt to adhere to and obey this mental activity as much as possible—subject to the same caveats.
Reasonism vividly contrasts the driving, energetic phenomenon which Aristotle called "man's rational faculty" with (reactive) emotions, (biological) drives, and (inborn) instincts. It argues that while these three should brightly inform and enlighten human action, the ultimate guide to thought and behavior should be reason alone. This is because only pure, clean, unadulterated, uncompromised reason is sublimely powerful and utterly trustworthy in uncovering truth—unlike emotions, drives, and instincts, or reasoning corrupted by them.
Reasonism is a scientific and philosophical thought-system which has immense trust and confidence (and "belief" and "faith") in cerebration, ratiocination, cogitation, rumination, reflection, deliberation, calculation, and analysis. But it summarily rejects faith, supernaturalism, revelation, intuition, superstition, and all other forms of nonsensicalness and irrationality. This includes blind, unthinking "belief" and acontextual, fanatical "conviction," as well as fantasy and delusion.
Reasonism is imminently empirical, common sensical, and practical. It emphatically rejects all Platonic and Kantian "forms" and "idealism" in which reality and reason don't touch each other. So too any other belief-system which considers fundamental and important issues without utilizing the senses, sensory input, evidence, and facts. So too any belief-systems in which the logic is insular, circular, and incestuous.
Reasonism has nothing to do with the phenomenon of psychological "rationalism" in which counterfeit reasoning involving convoluted logic results in false explanations, excuses, and justifications for generally strange and unjustifiable ideas and behaviors. Reasonism is also a kind of clean, clear, legitimate, logical version of philosophical "rationalism" in which the brain is no longer isolated from the universe or its perceptions of that universe. The mind isn't considered to be separate from or superior to sense perceptions when it comes to making judgments, gaining knowledge, and understanding reality. Reasonism says that the rational faculty and sensing apparatus of intelligent beings are wholly integrated units in complete contact with each other and the universe.
Reasonism also states that reason is the foundation of the glorious and transcendental phenomena known as science and philosophy, which highly efficaciously explain the physical and mental nature of our universe. The Greeks called reason logos, "the word," and correctly noted that it was the organizing and driving principle of the entire universe.