Speculative systems have in all ages of the world been adopted for reasons too frivolous to have determined the judgment of any man of common sense in a matter of the smallest pecuniary interest. Gross sophistry has scarce ever had any influence upon the opinions of mankind, except in matters of philosophy and speculation; and in these it has frequently had the greatest. The patrons of each system of natural and moral philosophy naturally endeavoured to expose the weakness of the arguments adduced to support the systems which were opposite to their own. In examining those arguments, they were necessarily led to consider the difference between a probable and a demonstrative argument, between a fallacious and a conclusive one: and Logic, or the science of the general principles of good and bad reasoning, necessarily arose out of the observations which a scrutiny of this kind gave occasion to.