How the Mind is to be known
The Personal Character of Consciousness.—Mind can be observed and known. But each one can know directly only his own mind, and not another's. You and I may look into each other's face and there guess the meaning that lies back of the smile or frown or flash of the eye, and so read something of the mind's activity. But neither directly meets the other's mind. I may learn to recognize your features, know your voice, respond to the clasp of your hand; but the mind, the consciousness, which does your thinking and feels your joys and sorrows, I can never know completely. Indeed I can never know your mind at all except through your bodily acts and expressions. Nor is there any way in which you can reveal your mind, your spiritual self, to me except through these means.
It follows therefore that only you can ever know you and only I can ever know I in any first-hand and immediate way. Between your consciousness and mine there exists a wide gap that cannot be bridged. Each of us lives apart. We are like ships that pass and hail each other in passing but do not touch. We may work together, live together, come to love or hate each other, and yet our inmost selves forever stand alone. They must live their own lives, think their own thoughts, and arrive at their own destiny.