18. Instinct being an unerring guide, when spirits resort to outward intelligence in the primary periods of their development, they are confounded sometimes by effects. There is, however, between these two principles a difference which it is necessary to consider.
Instinct is a sure guide, and always a good one. At a given time, it may become useless, but never hurtful. It is weakened by the predominance of intelligence.
The passions in the first expressions of the soul have this in common with instinct: they are guided by an equally involuntary force. They are born more particularly to supply the needs of the body, and depend more than instinct upon the organism. That which distinguishes them above all else from instinct, is that they are individual, and do not produce, as does instinct, general and uniform effects. We see them, on the contrary, varied in intensity of nature according to individual development. They are useful as stimulants; that is, until the awakening of the moral sense, which, in the case of a passive being, transforms him into a rational being. From this moment they become not only useless, but hurtful to the development of the spirit, whose upward progress they hold back; they are weakened by the development of reason.