Metaphysics is the study of pure concepts as they relate to moral or physical experience. The goal of the Grounding or the Metaphysics of Morals is to establish the "supreme principle of morality". Kant's purpose of this book is to develop a "pure" moral philosophy, a "metaphysics of morals" that relies on the priori concepts of reason, not empirical. Morality requires us to separate our rationality from our nature and act solely on the basis of logical principles. A morality based on reason would make sense to all people; Kant thinks it would therefore be superior to a moral system. Kant offers a formula to test an action, to see whether or not it is a pure motive resulting in moral worth. He calls this formula the categorical imperative; this may also be formulated as a requirement that we act only according to principles that could be laws in a "kingdom of ends". People must apply moral laws to many different situations and circumstances and developing a clear understanding of moral principles can help people keep track of their moral obligations. A clear understanding of morals can also help people to ensure that their motivations are pure. Actions are not truly moral if they only appear to conform to moral law but lack moral motivation. .
Kant tries to develop a moral philosophy that depends only on the fundamental concepts of reason. Kant presumes that moral principles must apply to all rational beings at all places and at all times. Moral principles must therefore be based on concepts of reason, as opposed to particularities of culture or personality. Moral principles come from reason and not from experience. Kant understands reason to be the source of fundamental truths that transcend culture and history. Rational ideas that make sense to all people, they are universal. If rationality is universal then it must be a superior moral law, "Kingdom of ends". A secure understanding of morality must be based on "pure" concepts of reason.