A mental act by which the mind attends to one aspect of a thing without attending to other aspects naturally present in the same object. On the first level of abstraction, the mind disregards individual material things and concentrates on some universal material nature such as water or color. On the second level, the mind concentrates on abstract quantity, such as circle, plane, or square. On the third level, proper to metaphysics, the mind disregards all matter and grasps its object without any necessary relation to matter, arriving at the knowledge of being, existence, substance, unity, and the like. It is by means of abstraction that human reason, apart from revelation, can arrive at the knowledge of God's existence, and his attributes of infinite wisdom, goodness, and power. Abstraction is, therefore, the underlying principle of natural theology.