However, as I do not wish to enter here into a discussion of the mind, a task which would demand much labor and be of no interest to the public, I shall admit the hypothesis that our most general and most necessary ideas--such as time, space, substance, and cause--exist originally in the mind; or, at least, are derived immediately from its constitution.
But it is a psychological fact none the less true, and one to which the philosophers have paid too little attention, that habit, like a second nature, has the power of fixing in the mind new categorical forms derived from the appearances which impress us, and by them usually stripped of objective reality, but whose influence over our judgments is no less predetermining than that of the original categories.

Hence we reason by the ETERNAL and ABSOLUTE laws of our mind, and at the same time by the secondary rules, ordinarily faulty, which are suggested to us by imperfect observation.

This is the most fecund source of false prejudices, and the permanent and often invincible cause of a multitude of errors.

The bias resulting from these prejudices is so strong that often, even when we are fighting against a principle which our mind thinks false, which is repugnant to our reason, and which our conscience disapproves, we defend it without knowing it, we reason in accordance with it, and we obey it while attacking it.

Enclosed within a circle, our mind revolves about itself, until a new observation, creating within us new ideas, brings to view an external principle which delivers us from the phantom by which our imagination is possessed.
Thus, we know to-day that, by the laws of a universal magnetism whose cause is still unknown, two bodies (no obstacle intervening) tend to unite by an accelerated impelling force which we call GRAVITATION.