Introduction
OBTAINING THE KNOWLEDGE OF THINGS, FOR THE INSTRUCTION BOTH OF OURSELVES AND OTHERS. It consists in the reflections which have been made on the four principal operations of the mind: conceiving (concevoir), judging, reasoning, and disposing (ordonner).
By conception is meant the simple view we have of the objects which are presented to our mind; as when, for instance, we think of THE SUN, THE EARTH, A TREE, A CIRCLE, A SQUARE, THOUGHT, BEING, without forming any determinate judgment concerning them; and the form through which we consider these things is called AN IDEA.
Judgment is that operation of the mind through which, joining different ideas together, it affirms or denies the one of the other; as when, for instance, having the ideas of the EARTH and ROUNDNESS, it affirms or denies of the earth that it is round.
Reasoning is that operation of the mind through which it forms one judgment from many others; as when, for instance, having judged that true virtue ought to be referred to God, and that the virtue of the heathens was not referred to him, we thence conclude that the virtue of the heathens was not true virtue.
By disposition is here meant that operation of the mind, by which, having on the same subject (the human body, for instance), different ideas, judgments, and reasonings, it disposes them in the manner best fitted for obtaining a knowledge of the subject. This is also called Method.
All these operations are performed naturally, and oftentimes better by those who are unacquainted with the rules of logic than by those who know them.
Thus logic consists, not in discovering the means of performing these operations, since nature alone furnishes these in giving us reason, but in reflecting on that which nature does within us, which is of service to us in the following respects: —
First, In assuring us that we employ reason aright; for the consideration of the rule which guides it, awakens within us fresh attention to its operations.
Second, In enabling us to discover and explain more easily any error or defect which may be found in the operations of our mind; for it often happens that we discover, by the light of nature alone, that a reasoning is false, without being able to determine how it is so, as those who are not skilled in painting may be sensible of defect in a picture, without being able, nevertheless, to explain what is the blemish which offends them.
Third, In making us better acquainted with the nature of our mind, by the reflections which we thus make on its operations. And this is, in itself, more excellent, considered merely in a speculative point of view, than the knowledge of all corporeal things, which are infinitely beneath those which are spiritual.
And if the reflections which we make on our thoughts referred to ourselves alone, it would suffice to consider them in themselves, without having recourse to words or any other signs. But since we are not able to express our thoughts to each other, unless they are accompanied with outward signs; and that this custom is so strong, that even when we think alone, things present themselves to our minds only in connection with the words to which we have been accustomed to have recourse in speaking to others;—it is necessary, in logic, to consider IDEAS in their connection with WORDS, and WORDS in their connection with IDEAS.
From what has been said, it follows that logic may be divided into four parts, according to the different reflections which are made on the four operations of the mind.