 The Rise of Scientific Philosophy (1951a), Reichenbach’s last and most successful popular book, presents his broad philosophical viewpoint in an accessible way. The English prose is more fluent than in earlier works, and occasionally almost as pithy as Russell’s. Four chapters of the book provide Reichenbach’s review of the history of philosophical pretensions to a priori knowledge in metaphysics, epistemology and ethics. Writing of Kant, Reichenbach instructs: “His cognitive a priori coincides with the physics of his time; his moral a priori, with the ethics of his social class. Let this coincidence be a warning to all those who claim to have found the ultimate truth.” (p. 61) Of Hamlet, Reichenbach writes “To be or not to be—that is not a question but a tautology.” (p. 250) Much of the remainder of the book consists of selective popular science summaries, amid simplified restatements of the views in The Philosophy of Space and Time (1928h), and Experience and Prediction (1938c). The news in the book is the extended discussion of ethics. In his contribution to the Schilpp volume (1939a) on John Dewey, Reichenbach had written at some length, and with considerable disdain, about Dewey’s ethical theory. (His personal relations with Dewey are unknown to us, but it is possible that Reichenbach knew and disapproved of Dewey’s enthusiasm for World War I.) About ethics, Reichenbach was at least as pragmatic as Dewey, but about metaethics, and in particular about the logical form of ethical sentences, he was in close accord with Charles Leslie Stevenson’s imperativism. To assert “X is good” is just to assert “I approve of X: Do so as well!” In The Rise of Scientific Philosophy he insists that ethical statements express “volitional decisions,” without truth values, that are not subject to empirical knowledge. The empirical issues of ethics are only the causal questions of relations of means to ends. Reichenbach allows a place for logic in reasoning from ethical premises to ethical conclusions, but he insists that the characteristic feature of ethical statements, and the proper conclusion of ethical reasoning, is a call to action. Whatever else they are, ethical claims are imperatives. His recommendation for resolving fundamental ethical disagreements is not philosophy or science, but “social friction.” In keeping with his politics, Reichenbach’s last practical advice was the same as Joe Hill’s: Organize! But Reichenbach’s deepest ethical injunction was implicit in his most popular book: to form beliefs, to judge them, to change them, to weigh actions, to distinguish real from merely verbal differences, by the canons of scientific philosophy. 