Immanuel Kant

Key ideas

Woken from his 'dogmatic slumber' by David Hume, Kant argued that the mind is not a passive receiver of experience. It actively structures what we perceive through space, time and categories such as cause and effect. We can therefore know the world as it appears to us with certainty, but never things as they are in themselves.

In ethics he held that the moral worth of an action lies in the principle it is done from, not its consequences. The supreme principle is the categorical imperative: act only on rules you could will everyone to follow, and treat humanity never merely as a means but always also as an end. This is the foundation of deontology and of the Kantian side in the main ethical theories, the trolley problem and many other debates.

He also held that morality presupposes freedom. As natural beings we are fully determined, but as rational agents we must regard ourselves as free, a position that still has defenders in the free will debate.

“Two things fill the mind with ever new and increasing admiration and awe, the oftener and the more steadily we reflect on them: the starry heavens above and the moral law within.”

Immanuel Kant, Critique of Practical Reason, Conclusion, trans. T. K. Abbott

Life, briefly

Kant spent his whole life in and around Königsberg, now Kaliningrad, where he was a popular lecturer on everything from logic to geography. His daily routine was so regular that neighbours were said to set their clocks by his afternoon walk.

He published the Critique of Pure Reason at fifty-seven, after more than a decade of near silence, and then produced his major works at remarkable speed over the next fifteen years.

Major works

• Critique of Pure Reason (1781)
• Groundwork of the Metaphysics of Morals (1785)
• Critique of Practical Reason (1788)
• Critique of Judgment (1790)

Schools of thought

Kantian ethics

Further reading

• EncyclopediaStanford Encyclopedia of Philosophy: Immanuel Kant
• WikipediaImmanuel Kant