CHAPTER II

Definition of Logic

IT is the province of Logic to distinguish correct from incorrect thoughts, i. e. to analyse those thoughts which are accepted by mankind as indubitably correct, and to point out wherein they differ from those which are regarded as doubtful or incorrect; and, as a consequence of this function, it is also its province to lay down rules for the attainment of correct thoughts and for the avoidance of incorrect thoughts. Thus Logic is both a Science and an Art. It is a Science, inasmuch as it furnishes us with a knowledge of what is, inasmuch as it is an analysis, and determines the conditions on which valid thoughts depend. It is an Art, inasmuch as it lays down rules for practice, and thus enables us to detect incorrect thoughts in the reasonings of others, and to avoid them in our own.

Logic may therefore be defined as the science of the conditions on which correct thoughts depend, and the art of attaining to correct and avoiding incorrect thoughts.

Note. This definition is in substance that given by Mr. Mill in his Examination of Sir W. Hamilton's

Philosophy, p. 391 (third ed., p. 448). 'Logic,' he says, 'is the art of thinking, which means of correct thinking, and the science of the conditions of correct thinking.' The word 'thoughts' is substituted for 'thinking,' in order to bring more prominently before the student, what Mr. Mill himself acknowledges, the fact that Logic is concerned with the products or results rather than with the process of thought, i. e. with thoughts rather than with thinking, though, in estimating the conditions on which correct thoughts depend, it is necessary, to some extent, to take account of the processes by which they are formed. It seems also desirable to introduce into the definition of Logic some reference to 'incorrect thoughts,' as bringing out more distinctly the character of Logic as an art, and asserting for it the right of investigating fallacies.

CHAPTER III

On the Relation of Thought to Language

WHETHER it is possible to think without the aid of language, is a question which has been a constant source of dispute amongst logicians and psychologists. It is not necessary, however, here to enter on this discussion. As all logicians are agreed that we cannot communicate our thoughts without the aid of language, or of equivalent signs, and that practically we do always think by means of language, by a sort of internal converse, it will be safer to adopt the terminology of those authors who regard our thoughts as expressed in language rather than that of those who consider or attempt to consider them in themselves as apart from their expression in words. I shall therefore speak of Terms and Propositions, not of Concepts and Judgments.

Note.-Sir W. Hamilton and his followers, regarding Logic as primarily and essentially concerned with thought, and only secondarily and accidentally with language, attempt to mark the products of thought by words which. do not imply their expression in language. Thus, instead

of Terms and Propositions, they use respectively the words Concepts and Judgments. The word Syllogism, owing to the ambiguity of the Greek word λóyos, stands either for the internal thought or the external expression of it. (See Hamilton's Lectures on Logic, Lecture i.)

CHAPTER IV

Division of the Products of Thought

IT has been stated that thought is the act or operation of comparison. Its simplest result is that which is expressed by the Term. Terms may be combined into Propositions, and Propositions, either singly or in conjunction with one or more other propositions, may lead to Inferences. I shall treat in order of the Term, of the Proposition, of Inferences. Before proceeding further, it may perhaps be useful to the student to give by anticipation instances of these products or results of thought. Man, good, manliness, goodness, the goodness of man, the virtue of manliness, are all instances of terms. This man is good,' 'All citizens of a state are under an obligation to obey its laws,' are instances of Propositions, and, according to logical phraseology, 'good' is said to be predicated of 'this man,' and 'under an obligation to obey its laws' is said to be predicated of all citizens of a state.' " The term predicated is called the Predicate, and the term of which it is predicated is called the Subject, the word 'is' or 'are' (or, in the case of negative propositions, 'is not' or 'are not'), which connects the two, being called the Copula. Lastly, we may take as instances of Inferences the following :—