Afterward the philosopher demonstrates to us the necessity of abstracting all personality from the exercises which combine for the attainment of common sense.
"There is," said he, "an obstacle against which all stupid people stumble; it is the act of reasoning under the influence of passion.
"Those who have not decided to renounce this method of arguing will never be able to give a just decision.
"There are self-evident facts, which certain people refuse to admit, because this statement of the truth offends their sympathies or impedes their hatreds, and they force themselves to deny the evidence, hoping thus to deceive others regarding it.
"But truth is always the strongest and they soon become the solitary dupes of their own wilful blindness.
"The man of common sense knows how to recognize falsehood wherever he meets it; he knows how vain it is to conceal a positive fact and also how dangerous it is to deceive oneself, a peril which increases in power, in proportion to the effort made to ignore it.
"He does not wish to imitate those pusillanimous people who prefer to live in the agony of doubt rather than to look misfortunes in the face. He who is determined to acquire common sense will use the following argument:
"Doubt is a conflict between two conclusions.
"So long as it exists it is impossible to adopt either.
"Serenity is unknown to those whom doubt attacks.