Let us assume that claims for knowledge are often made which do not amount to claims for perfect or demonstrable knowledge. Let us further assume that when such claims are suspect it is possible to examine them and, subsequently, to declare them sometimes just, sometimes not (roughly in the manner followed in law-courts). Let us call such claims for knowledge claims for imperfect knowledge, and assume that these are sometimes just. The question is, what does imperfect knowledge amount to? How do we demarcate imperfect knowledge from perfect knowledge and from mere conjecture? In what follows I shall criticize the popular theory that imperfect knowledge equals a high degree of rational belief. My own view will be (paragraph 13 below) that imperfect knowledge differs from perfect knowledge only in that it makes allowance for acts of God, so-called.