Like other words in current philosophical use, such as historicism and subjectivism, irrationalism is an exceedingly imprecise term that is employed with a wide variety of meanings and implications. Consequently, any attempt to elucidate its sense within the confines of a clear-cut and tidy formula quickly runs into difficulties. It might be said, for instance, that to describe a writer as an irrationalist is to speak of him as denying the authority of reason. But how is the notion of "reason" itself to be understood, and in what respects is its authority supposed to be flouted? It would scarcely be sufficient to reply that denial of reason consists in illogicality or confusion of thought, or that it manifests itself in a tendency to arrive at unacceptable conclusions; for this would apply to the work of many thinkers to whom the label "irrationalist" is clearly inapplicable. In addition, the...