Compared with men, it is probable that brutes neither attend to abstract characters, nor have associations by similarity. Their thoughts probably pass from one concrete object to its habitual concrete successor far more uniformly than is the case with us. In other words, their associations of ideas are almost exclusively by contiguity. So far, however, as any brute might think by abstract characters instead of by association of con cretes, he would have to be admitted to be a reasoner in the true human sense. How far this may take place is quite uncertain.

All our life, so far as it has definite form, is but a mass of habits.

The union of the mathematician with the poet, fervor with measure, passion with correctness, this surely is the ideal.

Truth is something that happens to an idea.

The function of ignoring, of inattention, is as vital a factor in mental progress as the function of attention itself.

The love of life, at any and every level of development, is the religious impulse.

Our lives are like islands in the sea, or like trees in the forest. The maple and the pine may whisper to each other with their leaves ... But the trees also commingle their roots in the darkness underground, and the islands also hang together through the ocean's bottom.