473. The reason why man is not sufficiently enlightened by his reason so as to know this, is that mistakes arising from believing in the appearances perceived by the body's external senses cast a shadow across that light. The reason why man cannot help feeling that it is his own life that makes him alive, is that the instrumental feels the principal as belonging to itself, so as to be unable to distinguish them. The principal and the instrumental causes act as a single cause according to a theorem well known to the learned. The principal cause is life, the instrumental cause is the human mind. Even animals seem to possess life created in them, but this is a similar fallacy, for they are organs created to receive light and heat from the natural world, and at the same time from the spiritual world. Each species is a form taken by some natural love, and it receives light and heat from the spiritual world transmitted through heaven and hell; through heaven in the case of gentle animals, through hell in the case of dangerous ones. Man is the only creature to receive light and heat, that is, wisdom and love, directly from the Lord, and this is the difference between man and animals.