It is quite true, as Abram Tucker puts it, that 'The science of abstruse learning, when completely attained, is like Achilles' spear, that healed the wounds it had made before; so this knowledge serves to repair the damage itself had occasioned, it casts no additional light upon the paths of life.' But few persons sensible of the value of exact knowledge will complain of the _necessary_ elaboration to which it sometimes leads. Nor will those who have felt the thrill of pleasure which complete analysis imparts, regret the patience which put them in possession of a secret of science, or made them master of a new field of knowledge. Common sense is the substratum of all logic. Common sense is the natural sense of mankind. It is founded on common observation and experience. It is modest and plain and unsophisticated. It sees with everybody's eyes and hears with everybody's ears. It has no capricious distinctions, no partialities, and no mysteries. It never equivocates and never trifles. Its language is always the same, and is always intelligible. It is known by its perspicuity of speech and singleness of purpose. The most prudent of all the children of fact, it never forsakes nature or reason. Some outline laws for its employment, if they can be indicated, must be better than its popular aimless and desultory use. PREFACE OF 1866. One has no right to make a literary subject political--that is, to make it partisan; but to give a political motive which concerns all equally, for promoting a literary study, is allowable, and does not partake of the nature of party politics. One may, like Cobbett, look on literature with political eyes, without, like him, making it a vehicle of party attacks. In this country, where the political genius of the people lies in self-government--where the public growth of the people and their internal liberty depend upon their capacity to manage their own affairs--the art of public speaking has political importance to every aide in politics. To be able to take a subject well in hand, like a stage-coach driver does his horses--to hold the reins of your arguments firmly--to direct and drive well home the burden of your meaning, is a power which every man ought to study to attain, who rises to address a council, or stands up on a platform to convince a meeting. A LOGIC OF FACTS. CHAPTER I. THE LOGIC OF THE SCHOOLS It is a humiliating reflection that mankind never reasoned so ill as when they most professed to cultivate the art of reasoning.--Life of Galileo, p. 1. society for the Diffusion of Useful Knowledge.