The name of the immortal element (in man) was not given to man as a gratuitous gift. It had to be gained, like the name of God, in the sweat of his face. Before man could say that he believed his soul to be immortal, he had to discover that there was a soul in man. It required as great an effort to form such a word as anima, breath, and to make it signify the infinite in man, as to form such a word as diva, bright, and to make it signify the infinite in nature.

Gifford Lectures, III.

To us the two words 'body and soul' are so familiar that it seems almost childish to ask how man came at first to speak of body and soul. But what did he mean by soul? What do we ourselves mean by soul? Think of the many meanings contained in our word soul. Our soul may mean the living soul; it may mean the sentient soul; it may mean the seat of the passions, whether good or bad; it may mean the organ of thought; and lastly, the immortal element in man. The question we have to ask is not how man arrived at a name for soul, but how he came for the first time to speak of something different from the body.

Gifford Lectures, III.

The discovery of the soul, the first attempts at naming the soul, started everywhere from the simplest observations of material facts. The lesson cannot be inculcated too often that the whole wealth of our most abstract and spiritual words comes from a small number of material or concrete terms.

Gifford Lectures, III.

We see that the way which led to the discovery of a soul was pointed out to man as clearly as was the way which led him to the discovery of the gods. It was chiefly the breath, which almost visibly left the body at the time of death, that suggested the name of breath, and afterwards the thought of something breathing, living, perceiving, willing, remembering, and thinking within us. The name came first, the name of the material breath. By dropping what seemed material even in this airy breath, there remained the first vague and airy concept of what we call soul.

Gifford Lectures, III.

The worship of the spirits of the departed which, under various forms, was so widely spread over the ancient world, could not but accustom the human mind to the idea that there was something in man which deserved such worship. The souls of the departed were lifted higher and higher, till at last they reached the highest stage which existed in the human mind, namely, that of divine beings, in the ancient sense of that word.