Ultimate interior principle of the life (ability to move self) of living bodies. There are three kinds of souls, vegetative or plant, animal, and rational (human). The soul is the “substantial form” of the living body, determining its species, e.g., geranium, dog, man. It is itself a substance and not an accident of the body; an incomplete substance, since it is by its nature destined for union with a body. According to Thomist doctrine, some disagreeing, there is in each living body only one substantial form, the soul, the principle of all informing, vivifying, and operating. The human or rational soul is the ultimate interior principle vivifying the human body and rendering man capable of performing all his vital acts. Pope Pius IX declared it to be Catholic doctrine that the rational soul is the true, per se, and immediate form of the body. The soul is the proper object of the science of psychology (Greek: psyche, soul). Unfortunately much of the science that goes under the name, is more physiology than psychology. The human soul is integrally simple, has no part outside of part; otherwise ideation, judging, and reasoning cannot be explained; is spiritual since its operations are spiritual, as knowing the spiritual, the abstract, and the universal, reflecting on self, enjoying spiritual things, exercising freedom; internally immortal since spiritual, and externally immortal since God will not annihilate it. Scripture clearly teaches its immortality. The human soul is in the whole body and in each part of the body. It is created by God and, according to the more common modern opinion, infused into the body at the first instant of the latter’s existence; created “to God’s image and likeness” since, similar to God, the soul is a spirit endowed with intellect and free will. The union between soul and body is substantial, resulting in one complete substance, which is a human person if we except the body and soul of Christ. Scripture informs us that the human soul will be judged after death, will be consigned to heaven or to hell, and on the Day of General Judgment renited with its body, the composite thenceforth to enjoy the Beatific Vision or to suffer the torments of the damned, for eternity.