Because people do not practice an objective method of gaining knowledge, they routinely accept bizarre, unproven assertions as possible. This destructive trend is promoted by two false ideas: rationalism and the arbitrary. Rationalism holds that knowledge is attained by ignoring reality while relying on deduction from arbitrarily formed concepts. We will see how modem philosophy's four schools (Pragmatism, Analysis, Logical Positivism, Existentialism) are based on and spread these bad ideas. We will cover Objectivism's answers to rationalism and the arbitrary, and demonstrate the role of these errors in generating modem evils such as political correctness and environmentalism. (A 1990 course expanded)