**'" *..*' ' " . 



2 NATUKB' AND DESIGN OF THIS WORK. [CHAP. I. 



have arisen among the disputes of the logicians, have outgrown 

 their origin, and given to successive ages of speculation their pe- 

 culiar bent and character. The eras of Porphyry and Proclus, 

 of Anselm and Abelard, of Ramus, and of Descartes, together 

 with the final protests of Bacon and Locke, rise up before the 

 mind as examples of the remoter influences of the study upon the 

 course of human thought, partly in suggesting topics fertile of 

 discussion, partly in provoking remonstrance against its own un- 

 due pretensions. The history of the theory of Probabilities, on 

 the other hand, has presented far more of that character of steady 

 growth which belongs to science. In its origin the early genius 

 of Pascal, in its maturer stages of development the most recon- 

 dite of all the mathematical speculations of Laplace, were direct- 

 ed to its improvement ; to omit here the mention of other names 

 scarcely less distinguished than these. As the study of Logic has 

 been remarkable for the kindred questions of Metaphysics to 

 which it has given occasion, so that of Probabilities also has been 

 remarkable for the impulse which it has bestowed upon the 

 higher departments of mathematical science. Each of these sub- 

 jects has, moreover, been justly regarded as having relation to a 

 speculative as well as to a practical end. To enable us to deduce 

 correct inferences from given premises is not the only object of 

 Logic ; nor is it the sole claim of the theory of Probabilities that 

 it teaches us how to establish the business of life assurance on a 

 secure basis ; and how to condense whatever is valuable in the 

 records of innumerable observations in astronomy, in physics, or 

 in that field of social inquiry which is fast assuming a character 

 of great importance. Both these studies have also an interest 

 of another kind, derived from the light which they shed upon 

 the intellectual powers. They instruct us concerning the mode 

 in which language and number serve as instrumental aids to the 

 processes of reasoning; they reveal to us in, some degree the 

 connexion between different powers of our common intellect ; 

 they set before us what, in the two domains of demonstrative and 

 of probable knowledge, are the essential standards of truth and 

 correctness, standards not derived from without, but deeply 

 founded in the constitution of the human faculties. These ends 

 of speculation yield neither in interest nor in dignity, nor yet, it 



