"It is only," said he, "where we are sufficiently permeated with all the principles of judgment that we shall be able to think of acquiring this quality, so necessary to the harmony of life. "The most important of all the mental operations which ought to be practised by him who desires common sense to reign supreme in all his actions and decisions, is incontestably deduction. "When the union of ideas, which judgment permits, is made with perception and exactness, there results always an analysis, which, if practised frequently, will end by becoming almost a mechanical act. "It is, however, well to study the phases of this analysis, in order to organize them methodically first. "Later, when the mind shall be sufficiently drilled in this kind of gymnastics, all their movements will be repeated in an almost unconscious way, and deduction, that essential principle of common sense, will be self-imposed. "In order that deductions may be a natural development, the element relating to those which should be the object of judgment should be grouped first. "The association of statements is an excellent method for it introduces into thought the existence of productive agents. "We have already spoken of the grouping of thoughts, which is a more synthetical form of that selection. "Instead of allowing it to be enlarged by touching lightly on all that which is connected with the subject, it is a question, on the contrary, of confining it to the facts relating to only one object. "These facts should be drawn from the domain of the past; by comparison, they can be brought to the domain of the present in order to be able to associate the former phenomena with those from which it is a question of drawing deductions. "It is rarely that these latter depend on one decision alone, even when they are presented under the form of a single negation or affirmation. "Deduction is always the result of many observations, formulated with great exactness, which common sense binds together. "That which is called a line of action is always suggested by the analysis of the events which were produced under circumstances analogous to those which exist now. "From the result of these observations, the habit of thinking permits of drawing deductions and common sense concludes the analysis. "The method of deduction rests upon this. "One thing being equal to a previous one should produce the same effects. "If we find ourselves faced by an incident that our memory can assimilate with another incident of the same kind, we must deduce the following chain of reasoning: "First, the incident of long ago has entailed inevitable consequences. "Secondly, the incident of to-day ought to produce the same effects, unless the circumstances which surround it are different. "It is then a question of analyzing the circumstances and of weighing the causes whose manifestation could determine a disparity in the results.