Page:An Investigation of the Laws of Thought (1854, Boole, investigationofl00boolrich).djvu/242

226 CHAPTER XV. THE ARISTOTELIAN LOGIC AND ITS MODERN EXTENSIONS, EXAMINED BY THE METHOD OF THIS TREATISE. HE logical system of Aristotle, modified in its details, but unchanged in its essential features, occupies so important a place in academical education, that some account of its nature, and some brief discussion of the leading problems which it presents, seem to be called for in the present work. It is, I trust, in no narrow or harshly critical spirit that I approach this task. My object, indeed, is not to institute any direct comparison between the time-honoured system of the schools and that of the present treatise; but, setting truth above all other considerations, to endeavour to exhibit the real nature of the ancient doctrine, and to remove one or two prevailing misapprehensions respecting its extent and sufficiency. That which may be regarded as essential in the spirit and procedure of the Aristotelian, and of all cognate systems of Logic, is the attempted classification of the allowable forms of inference, and the distinct reference of those forms, collectively or individually, to some general principle of an axiomatic nature, such as the "dictum of Aristotle:" Whatsoever is affirmed or denied of the genus may in the same sense be affirmed or denied of any species included under that genus. Concerning such general principles it may, I think, be observed, that they either state directly, but in an abstract form, the argument which they are supposed to elucidate, and, so stating that argument, affirm its validity; or involve in their expression technical terms which, after definition, conduct us again to the same point, viz., the abstract statement of the supposed allowable forms of inference. The idea of classification is thus a pervading element in those systems. Furthermore, they exhibit Logic as resolvable into two great branches, the one of which is occupied with the treatment of categorical, the other with that of hypothetical or