Kant developed his moral philosophy in three works: Groundwork of the Metaphysic of Morals (1785), Critique of Practical Reason (1788), and Metaphysics of Morals (1797).

In Groundwork, Kant' tries to convert our everyday, obvious, rational knowledge of morality into philosophical knowledge.
The latter two works used "practical reason", which is based only on things about which reason can tell us, and not deriving any principles from experience, to reach conclusions which can be applied to the world of experience (in the second part of The Metaphysics of Morals).

Kant is known for his theory that there is a single moral obligation, which he called the "Categorical Imperative", and is derived from the concept of duty.
Kant defines the demands of moral law as "categorical imperatives".
Categorical imperatives are principles that are intrinsically valid; they are good in and of themselves; they must be obeyed in all situations and circumstances, if our behavior is to observe the moral law.
The Categorical Imperative provides a test against which moral statements can be assessed.
Kant also stated that the moral means and ends can be applied to the categorical imperative, that rational beings can pursue certain "ends" using the appropriate "means".
Ends based on physical needs or wants create hypothetical imperatives.
The categorical imperative can only be based on something that is an "end in itself", that is, an end that is not a means to some other need, desire, or purpose.
Kant believed that the moral law is a principle of reason itself, and is not based on contingent facts about the world, such as what would make us happy, but to act on the moral law which has no other motive than "worthiness to be happy".
Accordingly, he believed that moral obligation applies only to rational agents.

Unlike a hypothetical imperative, a categorical imperative is an unconditional obligation; it has the force of an obligation regardless of our will or desires In Groundwork of the Metaphysic of Morals (1785) Kant enumerated three formulations of the categorical imperative that he believed to be roughly equivalent.
In the same book, Kant stated:
Act only according to that maxim whereby you can, at the same time, will that it should become a universal law.

According to Kant, one cannot make exceptions for oneself.
The philosophical maxim on which one acts should always be considered to be a universal law without exception.
One cannot allow oneself to do a particular action unless one thinks it appropriate that the reason for the action should become a universal law.
For example, one should not steal, however dire the circumstances—because, by permitting oneself to steal, one makes stealing a universally acceptable act.
This is the first formulation of the categorical imperative, often known as the universalizability principle.

Kant believed that, if an action is not done with the motive of duty, then it is without moral value.
He thought that every action should have pure intention behind it; otherwise, it is meaningless.
The final result is not the most important aspect of an action; rather, how the person feels while carrying out the action is the time when value is attached to the result.

In Groundwork of the Metaphysic of Morals, Kant also posited the "counter-utilitarian idea that there is a difference between preferences and values, and that considerations of individual rights temper calculations of aggregate utility", a concept that is an axiom in economics:
Everything has either a price or a dignity.
Whatever has a price can be replaced by something else as its equivalent; on the other hand, whatever is above all price, and therefore admits of no equivalent, has a dignity.
But that which constitutes the condition under which alone something can be an end in itself does not have mere relative worth, i.e., price, but an intrinsic worth, i.e., a dignity. (
p. 53, italics in original).

A phrase quoted by Kant, which is used to summarize the counter-utilitarian nature of his moral philosophy, is Fiat justitia, pereat mundus, ("Let justice be
Kant developed his moral philosophy in three works: Groundwork of the Metaphysic of Morals (1785), Critique of Practical Reason (1788), and Metaphysics of Morals (1797).
In Groundwork, Kant' tries to convert our everyday, obvious, rational knowledge of morality into philosophical knowledge. The latter two works used "practical reason", which is based only on things about which reason can tell us, and not deriving any principles from experience, to reach conclusions which can be applied to the world of experience (in the second part of The Metaphysics of Morals).
Kant is known for his theory that there is a single moral obligation, which he called the "Categorical Imperative", and is derived from the concept of duty. Kant defines the demands of moral law as "categorical imperatives". Categorical imperatives are principles that are intrinsically valid; they are good in and of themselves; they must be obeyed in all situations and circumstances, if our behavior is to observe the moral law. The Categorical Imperative provides a test against which moral statements can be assessed. Kant also stated that the moral means and ends can be applied to the categorical imperative, that rational beings can pursue certain "ends" using the appropriate "means". Ends based on physical needs or wants create hypothetical imperatives. The categorical imperative can only be based on something that is an "end in itself", that is, an end that is not a means to some other need, desire, or purpose. Kant believed that the moral law is a principle of reason itself, and is not based on contingent facts about the world, such as what would make us happy, but to act on the moral law which has no other motive than "worthiness to be happy". Accordingly, he believed that moral obligation applies only to rational agents.
Unlike a hypothetical imperative, a categorical imperative is an unconditional obligation; it has the force of an obligation regardless of our will or desires In Groundwork of the Metaphysic of Morals (1785) Kant enumerated three formulations of the categorical imperative that he believed to be roughly equivalent. In the same book, Kant stated:
Act only according to that maxim whereby you can, at the same time, will that it should become a universal law.
According to Kant, one cannot make exceptions for oneself. The philosophical maxim on which one acts should always be considered to be a universal law without exception. One cannot allow oneself to do a particular action unless one thinks it appropriate that the reason for the action should become a universal law. For example, one should not steal, however dire the circumstances—because, by permitting oneself to steal, one makes stealing a universally acceptable act. This is the first formulation of the categorical imperative, often known as the universalizability principle.
Kant believed that, if an action is not done with the motive of duty, then it is without moral value. He thought that every action should have pure intention behind it; otherwise, it is meaningless. The final result is not the most important aspect of an action; rather, how the person feels while carrying out the action is the time when value is attached to the result.
In Groundwork of the Metaphysic of Morals, Kant also posited the "counter-utilitarian idea that there is a difference between preferences and values, and that considerations of individual rights temper calculations of aggregate utility", a concept that is an axiom in economics:
Everything has either a price or a dignity. Whatever has a price can be replaced by something else as its equivalent; on the other hand, whatever is above all price, and therefore admits of no equivalent, has a dignity. But that which constitutes the condition under which alone something can be an end in itself does not have mere relative worth, i.e., price, but an intrinsic worth, i.e., a dignity. (p. 53, italics in original).
A phrase quoted by Kant, which is used to summarize the counter-utilitarian nature of his moral philosophy, is Fiat justitia, pereat mundus, ("Let justice be
Immanuel Kant