What Kant calls a moral law that is universal.  It was his attempt to develop moral philosophy on the basis of pure reason. He had already written “A critique of pure reason” in which he recognized that the existence of god and individual freedom were not able to be inferred from logic (despite efforts by Descartes, etc).

Rousseau had already questioned the value of happiness (too vulnerable to comparison with others), Hume had already given up on reason alone as a basis for ethics.

Described in the “Groundwork for a metaphysics of morals”.

His first formulation appealed to certain principles being universally applicable, to any rational being (even an animal, or alien).  eg deception, theft, suicide, laziness, charity.  He accepts that some of these are “imperfect”, ie depends on the energy of the individual to what degree/extent.

His second formulation appealed to the idea of human dignity – that all rational beings are intrinsically valuable, and therefore should be accorded respect and never treated only as a means.  We also owe the same respect to ourselves as to others.

His third formulation describes autonomy, that we are free to make decisions, and that it is the good intention that makes a choice moral rather than simply following a rule/code even if laid down by god.

Not the same as the golden rule “Treat others as you would have them treat you” – as this allows for callousness: I would be disgusted with myself, so I won’t help them”.

Lived a very frugal life, but his ethics can seem very dutiful, even extreme – never to lie, even to save a life (because where else do you draw the line?).  Is very vague on the role of God – seems to think it a good idea but not necessary.

Provides the basis for human rights, and avoids the calculus associated with utilitarianism that can devalue human lives.  His emphasis on autonomy then leads on to existentialism through Kierkegaard, Nietzsche and Sartre (although without the reason).