Königsberg, 1724–1804
Immanuel Kant
Hume, Kant said, woke him from his dogmatic slumber. His answer was a revolution: we do not learn the order of nature from experience, because the mind puts that order there. Experience is something we make.
The view
Kant spent his whole life in Königsberg, a Baltic port then in Prussia, and published the Critique of Pure Reason in 1781, at the age of fifty-seven. It starts from a puzzle that Hume had made urgent. Geometry and Newton's physics seemed to Kant plainly certain and plainly about the world. Yet certainty cannot come from experience, as Hume had shown, and a truth of mere logic tells us nothing about the world. How can anything be both?
His answer is that such truths describe the equipment we bring to experience. Until now, he says, it was assumed that our knowledge must conform to objects. Suppose instead that objects, as we experience them, must conform to our knowledge. He compares the move to Copernicus, who explained the motions of the heavens by the motion of the observer.
The argument
Experience has two ingredients. The senses deliver raw material, and the mind gives it shape. Space and time are the forms in which anything can appear to us at all. A set of basic concepts, the categories, with cause and substance among them, are the rules by which the understanding binds appearances into a world of lasting objects and lawful events.
Thoughts without content are empty; intuitions without concepts are blind. Critique of Pure Reason A51/B75
This answers Hume. We can be certain that every event has a cause, because nothing could count as an experienced event unless the mind had already ordered it causally. Euclid's geometry is certain because it describes the form of our own outer sense.
The price is a boundary. We know things only as they appear under our forms. What they are in themselves, apart from any observer, we can never know. When reason tries to cross that line, to settle whether the world had a beginning or whether the soul is immortal, it falls into contradictions.
Where he meets Deutsch
Kant demolished the passive mind. Observation is not the starting point of knowledge, because nothing can be observed until a framework of theory is in place. Popper called himself an unorthodox Kantian for that reason, and Deutsch's account of observation as theory-laden descends from the same insight. Laws are not read off nature. In a sense the intellect prescribes them.
Kant also gave the Enlightenment its motto: dare to know, and have the courage to use your own understanding.
Where they part
Kant thought the framework was fixed, the same in every human mind, and guaranteed. He chose the best science of his day, Euclid and Newton, and declared it necessary. Within a century mathematicians had built consistent geometries that deny Euclid's parallel postulate, and in 1915 Einstein showed that physical space is one of them. The frame that could not be otherwise was otherwise.
Popper's correction is the one Deutsch adopts. The mind does impose its laws on nature, but as conjectures, and nature is free to refuse them. Our inborn expectations are fallible guesses supplied by evolution, and our scientific frameworks are fallible guesses supplied by us. Both can be replaced by better ones.
That removes the boundary too. Kant fenced off things in themselves as unknowable for ever. Deutsch rejects any such fence. If we can swap one framework for a better one, there is no fixed set of spectacles to be trapped behind, and no limit in principle to what explanation can reach.
| Kant | Deutsch | |
|---|---|---|
| Where does knowledge come from? | Experience supplies the matter; the mind supplies the form. | Conjecture: guesses, improved by criticism and experiment. |
| What does justification do? | The mind's categories are proved necessary for any experience at all. | Nothing. No theory is ever justified, and none needs to be. |
| Can knowledge grow without limit? | No. Things as they are in themselves lie beyond all possible knowledge. | Yes. Problems are inevitable, and problems are soluble. |
| What is knowledge, physically? | No physical account. The knowing subject stands outside the nature it orders. | Information that, once embodied, tends to keep itself in existence. |
Further reading
- Immanuel Kant, Critique of Pure Reason, translated by Paul Guyer and Allen Wood (Cambridge, 1998); and the shorter Prolegomena to Any Future Metaphysics (1783).
- Karl Popper, "Kant's Critique and Cosmology", chapter 7 of Conjectures and Refutations (1963).
- Immanuel Kant, Stanford Encyclopedia of Philosophy.