association, as we have already had occasion to notice But what opportunity can there possibly be for the operation of these principles, when the mind is called to fasten itself upon a subject, and to decide upon that subject, without any knowledge of those circumstances which may be directly embraced in it, or of its relations and tendencies?

(2.) The power of reasoning will depend, in the second place, on the power of attention and memory. There are some persons who seem to have no command of the ATTENTION. Everything interests them slightly, and nothing in a high degree. They are animated by no strong feeling; and enter into no subject requiring long-continued and abstract investigation with a suitable intensity of ardour. A defective remembrance of the numerous facts and propositions which come under review is the natural consequence of this. And this necessarily implies a perplexed and diminished power of ratiocination.

(3.) A third ground of difference is diversity in the susceptibility of feeling relations. The remark has already been made, (§ 138,) that facts may be accumulated having close and decisive relations to the points to be proved, but that they can never be so bound together as to result in any conclusion, without a perception or feeling of those relations. But it is well known, whatever it may be owing to, that the relations of objects are much more readily and clearly perceived by some than by others. As, therefore, every train of reasoning implies a succession or series of relative perceptions, a defect in the power of relative suggestion necessarily implies a defect in the reasoning power. And, on the other hand, a great quickness and clearness in the perception of relations is necessarily attended (other things being equal) with an augmented efficiency of reasoning.

§ 182. Of habits of reasoning.

But whatever may be the mental traits that render, in particular cases, the reasoning power more or less efficient, its efficacy will undoubtedly depend, in a great degree, on Habit. The effect of frequent practice, resulting in what is termed a HABIT, is often witnessed in those who

per

follow any mechanic calling, where we find that what was once done with difficulty comes in time to be done with great ease and readiness. The muscles of such sons seem to move with a kind of instinctive facility and accuracy in the performance of those works to which they have been for a long time addicted.

There is a similar effect of frequent practice in the increase of quickness and facility in our mental operations; and certainly as much so in those which are implied in reasoning as in any others. If, for instance, a person has never been in the habit of going through geometrical demonstrations, he finds his mind very slowly and with difficulty advancing from one step to another; while, on the other hand, a person who has so often practised this species of argumentation as to have formed a habit, advances forward from one part of the train of reasoning to another with great rapidity and delight. And the result is the same in any process of moral reasoning. In the prosecution of any argument of a moral nature, there is necessarily a mental perception of the congruity of its several parts, or of the agreement of the succeeding proposition with that which went before. The degree of readiness in bringing together propositions, and in putting forth such perceptions, will greatly depend on the degree of practice.

183. Of reasoning in connexion with language or expression. Language is the great instrument of reasoning. There may indeed be a deductive process which is purely mental; but, in point of fact, this is seldom the case. In the use of language, it is worthy of notice, that there is often a want of correspondence between the purely mental process in reasoning and the outward verbal expression of it. When persons are called upon to state their arguments suddenly and in public debate, they often commit errors which are at variance with the prevalent opinion of their good sense and mental ability. This is particularly true of men who are chiefly engaged in the ordinary business of life, or are in any situation where there is a constant call for action. The conclusions at which such persons arrive may be supposed to be generally correct, but they

frequently find themselves unable to state clearly and correctly to others the process of reasoning by which they arrived at them.-Oliver Cromwell, the famous English Protector, is said to have been a person to whom this statement would well apply. The complicated incidents of his life, and the perplexities of his situation, and his great success, sufficiently evince that he possessed a clear insight into events, and was in no respect deficient in understanding; but when he attempted to express his opinions in the presence of others, and to explain himself on questions of policy, he was confused and obscure. His mind eadily insinuated itself into the intricacies of a subject; and while he could assert with confidence that he had arrived at a satisfactory conclusion, he could not so readily describe either the direction he had taken, or the involutions of the journey.-" All accounts," says Mr Hume," agree in ascribing to Cromwell a tiresome, dark, unintelligible elocution, even when he had no intention to disguise his meaning; yet no man's actions were ever, in such a variety of difficult cases, more decisive and judi

cious,"

§ 184. Illustration of the foregoing section.

Such instances are not unfrequent. Mr. Stewart somewhere mentions the case of an English officer, a friend of Lord Mansfield, who had been appointed to the government of Jamaica. The officer expressed some doubts of his competency to preside in the court of chancery. Mansfield assured him that he would not find the difficulty so great as he imagined.-"Trust," said he, " to your own good sense in forming your opinions, but beware of stating the grounds of your judgments. The judgments will probably be right; the arguments will infallibly be wrong."

The perplexity, which is so often experienced by men engaged in active life, in giving a prompt and correct verbal expression to the internal trains of thought, is proba bly owing in part to a want of practice of that kind, and in part to certain mental habits, which they have been led, from their situation, to form and strengthen. In a thousand emergencies they have been obliged to act with

quickness, and, at the same time, with caution; in other words, to examine subjects, and to do it with expedition. In this way they have acquired exceeding readiness in all their mental acts. The consequence of this is, that the numerous minute circumstances, involved more or less in all subjects of difficult inquiry, are passed in review with such rapidity, and are made in so very small a degree the objects of separate attention, that they vanish and are forgotten. Hence these persons, although the conclusion to which they have come be satisfactory, are unable to state to others all the subordinate steps in the argument. Everything has once been distinctly and fairly before their own minds, although with that great rapidity which is always implied in a HABIT; but their argument, as stated in words, owing to their inability to arrest and imbody all the evanescent processes of thought, appears to others defective and confused.

CHAPTER X.

DEMONSTRATIVE REASONING.

185. Of the subjects of demonstrative reasoning.

In the remarks which have hitherto been made, the subject of reasoning has been taken up in the most general point of view. The considerations that have been proposed are applicable, in the main, to reasoning in all its forms. But it is necessary, in order to possess a more full and satisfactory conception of this subject, to examine it under the two prominent heads of Moral and Demonstrative.

There are various particulars in which moral and demonstrative reasoning differ from each other; the consideration of which will suggest more fully their distinctive nature. Among other things, DEMONSTRATIVE reasoning differs from any other species of reasoning in the subjects about which it is employed. The subjects are abstract ideas, and the necessary relations among them. Those

ideas or thoughts are called abstract which are representative of such qualities and properties in objects as can be distinctly examined by the mind separate from other qualities and properties with which they are commonly united. And there may be reckoned, as coming within this class of subjects, the properties of numbers and of geometrical figures; also extension, duration, weight, velocity, forces, &c., so far as they are susceptible of being accurately expressed by numbers or other mathematical signs. But the subjects of moral reasoning, upon which we are to remark hereafter more particularly, are matters of fact, including their connexion with other facts, whether cónstant or variable, and all attendant circumstances.-That the exterior angle of a triangle is equal to both the interior and opposite angles, is a truth which comes within the province of demonstration. That Homer was the author of the Iliad, that Xerxes invaded Greece, &c., are inquiries belonging to moral reasoning.

186. Use of definitions and axioms in demonstrative reasoning.

In every process of reasoning, there must be, at the commencement of it, something to be proved; there must also be some things, either known or taken for granted as suck with which the comparison of the propositions begins. The preliminary truths in demonstrative reasonings are involved in such definitions as are found in all mathematical treatises. It is impossible to give a demonstration of the properties of a circle, parabola, ellipse, or other mathematical figure, without first having given a definition of them. DEFINITIONS, therefore, are the facts assumed, the FIRST PRINCIPLES in demonstrative reasoning, from which, by means of the subsequent steps, the conclusion is derived. We find something entirely similar in respect to subjects which admit of the application of a different form of reasoning. Thus, in Natural Philosophy, the general facts in relation to the gravity and elasticity of the air may be considered as first principles. From these principles in Physics are deduced, as consequences, the suspension of the mercury in the barometer, and its fall when carried up to an eminence.

We must not forget here the use of axioms in the dem