Immanuel Kant (1724–1804) tries to explain how objective knowledge is possible after Hume undermined the idea that necessities such as causation are simply read from experience.

Big idea: The mind is not a blank camera pointed at a fully pre-structured world. Human experience has a form partly contributed by the cognitive conditions under which anything can appear to us as an object at all.

Kant calls space and time forms of intuition and describes categories such as causality as conditions organizing experience. That is his “Copernican” shift: instead of assuming cognition must conform passively to objects as they are in themselves, ask how objects as experienced conform to the structure of cognition.

This produces the famous distinction between:

• phenomena — things as they appear within the conditions of possible human experience;
• things in themselves (noumena) — reality considered independently of those conditions, which Kant argues we cannot know in the same way.

In ethics, Kant grounds morality in autonomy and rational consistency. One formulation of the categorical imperative says to act only on a maxim you could will as a universal law; another says to treat humanity never merely as a means but also as an end.

A misconception: Kant is not saying “reality is just made up by your mind.” He is trying to distinguish the contribution of the knowing subject from whatever exists independently of us.