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Rh the entire undertaking is informed with what might be called a practical purpose. The subject of discussion is the rights and wrongs of Casuistry, or of the Socratic demand for Definitions and Distinctions in our thinking; and, near the close of an inquiry which has never lost sight of this aim, the author says, "One main purpose of our inquiry was to raise at the end the question how far reasoned doubt must triumph over certainty, and whether a casuistic treatment of definitions need or need not eat the heart out of the faiths we live by" (p. 200). Again, "the chief incidental aims" of the book are described as "reflections on controversy, on the faults of language, and on the conflict between the rival ideals, faith and doubt" (p. 235).

The treatise might be described as a plea for what the author calls the "rough distinction." This is defined by Mr. Sidgwick as "a distinction where the contrasted notions, even at their sharpest (A and Non-A), cannot be applied with perfect exactness to actual cases, . . . but where a certain proportion of them belong to a doubtful borderland" (pp. 15, 16). Or "a rough distinction is a distinction that depends on a difference of degree" (p. 16). It is only in virtue of its applicability to concrete cases, or the reverse, that a distinction can be called "sharp" or "rough"; "ideally, there is never any difficulty about a distinction; whatever difficulty there is attaches only to its application" (p. 22). Mr. Sidgwick's purpose is "to show the extent and importance of unreal [or artificially sharp] distinctions — that is to say, of the disagreement between definite language and fluid facts . . . how far it is to be regarded as one of the permanent sources of faulty thinking and of needless heat of controversy" (pp. 78, 79). In the taking for "real" what are "unreal" distinctions, he finds the chief source of Ambiguity. "Ambiguity, in its most effective and troublesome form, arises out of the 'real' roughness of distinctions that are drawn by language as if they were perfectly sharp" (pp. 7, 8). What, then, he asks, are "the uses and abuses of rough distinction"? More particularly, how does language "act as a drag upon the progress of knowledge"? For "we are all too ready to see in words a mysterious datum behind which it is impossible to go. It takes a long apprenticeship to realities before we begin to get free from this illusion" (p. 20).

The author bases this doctrine of the real "roughness" of distinctions upon the principle of the "Continuity of Nature." "Nature is full of examples of a development which appears in our clumsy and rigid language as self-contradiction. Every child that outgrows childhood, every seed or germ that becomes other than seed or germ, every fact that changes its character in the least degree, proves to us daily that the 'Laws of Thought,' those pillars of elementary logic, are too ideal and abstract to be interpreted as referring to the actual things or particular