Immanuel Kant regards the moral law imposed by practical reason as Categorical Imperative. Categorical Imperative is the internal law imposed by conscience upon itself. Kant distinguishes Categorical Imperatives from Hypothetical Imperatives.
A hypothetical imperative is assertorial. It is an assertion of fact. e.g The psychological law, “ All persons act to relieve a feeling of want”. It is a statement of fact. Moral law is an imperative or command which should be necessarily obeyed. It is not an assertion but a statement of standard
A hypothetical imperative is conditional. It is a means to some other end. If we want to enjoy good health, we must observe the laws of hygiene. Moral law is categorical i.e. it is unconditional. It is not a means to some other goals. It is an end in itself. It admits no questions. It demands unconditional obedience.
A hypothetical imperative is derivative. Natural laws are derived from experience. It depends upon empirical facts for its obedience. Moral law is a priori. It is not derived from experience. It is known through reason.
A hypothetical imperative can be set aside by more higher laws. If the circumstances change, it may change. Moral law cannot be set aside by any higher laws. It is the Categorical imperative and ought to be followed in all situations.
A hypothetical imperative is relative and subjective. It applies to different individuals in different forms. Moral law or categorical imperative is to be obeyed universally. It applies to all persons. It is command to all rational beings.