Douglas Clyde Macintosh was an epochal philosopher-theologian who responded to challenge from his brother and at the University of Chicago find a basis for religion other than authority and tradition. Ontario born and McMaster educated, he explored the modern isms: scepticisms, agnosticisms, empiricisms, philosophical idealisms, pragmatisms, Ritschlian value theologies, mysticisms, contemporary realisms, and, later, process philosophies, phenomenologies, and existentialisms. A monistic critical realism which combined science with common sense realism and epistemological discrimination he found to be an adequate grounding for daily living, human values, personal theological thought, and social issues.