Activity is the faculty by which we act in the world, and it has three different forms – will (activity that's voluntary), instinct (activity that's never been voluntary), and habit (activity that was once voluntary but is no longer). We'll begin with instinct.

What distinguishes the actions caused by instinct is that they're not determined by prior experience. Instinct plays an especially important role in the lives of animals, which are, in fact, little more than the playing out of a series of instincts. But instinct also plays a more limited role in the lives of children, one that diminishes as they grow older. It's instinct that drives the child to its mother's breast, for example, to do what it must to draw sustenance. In adults, however, instinct plays a smaller role, and even the instinct of self-preservation diminishes in significance.

Here are the principal characteristics of instinctive activity:

1. Unconsciousness. When they act instinctively, animals are conscious of the movements they engage in but not of the ends they serve. Were this not the case, we'd have to grant them greater foresight than we ourselves possess. An animal might eat by instinct but not with the express purpose of survival.

2. Perfection. Instincts are perfect – their means are perfectly tailored to the ends they're designed to achieve. This perfection exists from the first day of the being's life and isn't a function of education or experience.

3. […]