This chapter examines the leading rationalists of the seventeenth, eighteenth, and nineteenth centuries. It looks at the implications of rational philosophy for psychology. Rationalism and empiricism result in contrasting views of human beings and in different philosophies of science. Rene Descartes is regarded as a rationalist because he promoted reason as the means of attaining foundational scientific knowledge. His major works emphasize innate ideas, a priori truths, and a preference for deduction. In this philosophical context, his method is grounded in a rebellion against skepticism. The scientist or the rationalist can discover as much or more about God as the theologian. Baruch Spinoza's rationalism is evident in his use of the geometric method. His ideas were often set forth in terms of axioms, numbered propositions, and demonstrations. The empiricists and rationalists disagreed on many things, but they shared in a new interpretation of the role of human curiosity.