The basic question of this monograph is: how should we go about judging arguments to be reasonable or unreasonable? Our concern will be with argument in a broad sense, with realistic arguments in natural language. The basic object will be to engage in a normative study of determining what factors, standards, or procedures should be adopted or appealed to in evaluating an argument as good, not-so-good, open to criticism, fallacious, and so forth. Hence our primary concern will be with the problems of how to criticize an argument, and when a criticism is reasonably justified.