13. According to another system, instinct and intelligence have one and the same principle alone. Having arrived at a certain degree of development, this principle, which at first had only the qualities of instinct, is subject to a transformation which imparts to its free intelligence.
If this were true, for the intelligent man who loses his ability to reason, and is guided exclusively by instinct, his intelligence would regress to its primitive state; and, upon recovering his ability to reason, his instinct would, once again, turn back into the state of intelligence; this cycle would repeat itself, alternatively, for each bout of rage encountered. This is not admissible.
Incidentally, intelligence and instinct are frequently present, side-by-side, in the same action. For instance, upon walking a man’s legs move in an instinctive way; mechanically, he places one foot before the other, without thinking of it. However, when he wants to accelerate or lessen his pace, lift up his foot, or deviate it in order to avoid an obstacle, there is calculation and combination involved; he acts here with a deliberate purpose. The involuntary impulsion of the movement is the instinctive act; whereas the calculated direction of the movement is the intelligent act. A carnivorous animal is compelled by its instinct to gain nourishment from meat; but the precautions it takes, its foresight of possible eventualities - which varies according to the circumstances - in order to capture his prey, are acts of intelligence.