“The difference between men is in their principle of association. Some men classify objects by color and size and other accidents of appearance; others by intrinsic likeness, or by the relation of cause and effect. The progress of the intellect is to the clearer vision of causes, which neglects surface differences. To the poet, to the philosopher, to the saint, all things are friendly and sacred, all events profitable, all days holy, all men divine. For the eye is fastened on the life, and slights the circumstance. Every chemical substance, every plant, every animal in its growth, teaches the unity of cause, the variety of appearance.”