The instruments are in the external body, the gross body of man; but the mind and the intellect are not. They are in what is called in Hindu philosophy the finer body; and what in Christian theology you read of as the spiritual body of man; finer, very much finer than the body, and yet not the soul. This soul is beyond them all. The external body perishes in a few years; any simple cause may disturb and destroy it. The finer body is not so easily perishable; yet it sometimes degenerates, and at other times becomes strong. We see how, in the old man, the mind loses its strength, how, when the body is vigorous, the mind becomes vigorous, how various medicines and drugs affect it, how everything external acts on it, and how it reacts on the external world. Just as the body has its progress and decadence, so also has the mind, and, therefore, the mind is not the soul, because the soul can neither decay nor degenerate. How can we know that? How can we know that there is something behind this mind? Because knowledge which is self-illuminating and the basis of intelligence cannot belong to dull, dead matter. Never was seen any gross matter which had intelligence as its own essence. No dull or dead matter can illumine itself. It is intelligence that illumines all matter.