Immanuel Kant

Long before he became the "giant of Königsberg" in philosophy, Kant was a deeply insightful natural scientist. In 1755, he proposed the nebular hypothesis, correctly deducing that the Solar System formed from a massive cloud of gas and that the Milky Way was a spinning disk of stars. He even theorized that other distant nebulae were actually separate "island universes" or galaxies, a view not proven until the 20th century.

His scientific curiosity extended to Earth’s mechanics. He was the first to argue that the Moon’s gravity slows the Earth’s rotation through tidal friction and offered one of the first systematic, non-supernatural explanations for earthquakes. This "pre-critical" period shows a mind obsessed with the underlying laws of the physical world before he turned his attention to the laws of the mind itself.

Kant’s greatest breakthrough was "transcendental idealism," a theory that revolutionized how we understand experience. He argued that we never see "things-in-themselves"; instead, our minds act as a filter. Space and time aren't external containers we live in; they are "forms of intuition"—built-in software that our brains use to organize sensory data.

He called this his "Copernican Revolution." Just as Copernicus realized the Earth moves around the Sun, Kant realized that objects must conform to our understanding, not the other way around. This solved the skepticism of David Hume, who had argued we can't truly "know" cause and effect. Kant countered that we know cause and effect because our minds are the ones imposing that logic on the world to make sense of it.

Kant spent nearly his entire life in Königsberg, Prussia, rarely traveling more than a few miles from his home. He lived with a rigid, monastic consistency: waking at 5:00 AM, lecturing, writing, and taking a daily walk at the exact same time every afternoon. Despite this austerity, he was a popular social figure, known for hosting lively dinner parties where he engaged with the city's intellectual and Masonic circles.

This disciplined lifestyle was mirrored in his work ethic. He famously remained silent for a decade while "awakening from his dogmatic slumber" to write the Critique of Pure Reason. When he finally emerged in 1781, he produced a series of massive, dense volumes that laid the foundation for almost all subsequent Western philosophy, from ethics to aesthetics.

In his moral philosophy, Kant argued that right and wrong are not determined by consequences or emotions, but by reason. He believed in a "categorical imperative"—the idea that you should only act according to rules that you would want to become universal laws. This focus on duty and autonomy made the individual the ultimate source of moral authority.

This logic extended to his politics. He was a champion of the Enlightenment, proposing that "Perpetual Peace" could be achieved if every state became a republic and joined an international federation. While he was a man of his time—promulgating scientific racism for much of his career—he notably moved away from those views in his final decade, advocating for a more inclusive cosmopolitanism.