A review of Critique of Pure Reason

To be real, I didn't fully realise what I was getting myself into with this one. It's not for the weak.

It's incredibly dense, though not impossibly difficult. There is so much meaning and ideas is packed into almost every sentence. Kant introduces an ENORMOUS number of concepts and definitions, then spends the book applying them in increasingly elaborate arguments. It takes time to get used to his terminology, and I'll be honest, he isn't the clearest writer (though I've heard from the streets that the original German is even worse). I even switched midway from the Penguin to the Cambridge edition, hoping it would help, but it didn't much.

What kept me going though was realising that so many of the esoteric thoughts I've had about reality, the limits of knowledge, and questions beyond human experience were being examined with a depth and precision I never imagined possible. Questions i struggled even to articulate were being systematically dissected by someone writing in the 1700s. I could see why this is considered a cornerstone of Western philosophy.

It's funny though, the whole book is Kant asking whether we can truly KNOW anything a priori, independently of experience. The reality is the answer is not as definitive as you might think and way more nuanced.

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Hard to really summarise the book, but the following is the distillation of all the notes I took whilst reading the book.

The core of the book is an attempt to understand what human reason (our drive to seek ultimate explanations) can tell us about the world, and where its limits lie. It's like trying to observe the observer, while recognising that observation has its own limits.

We experience reality through space and time, and our understanding makes sense of it through categories like causality. Mathematics constructs concepts in pure intuition (our built in sense of space and time), which lets it establish truths that genuinely expand knowledge.
Natural science applies the categories to possible experience to discover laws of nature. But reason wants to go further, toward a complete picture and an ultimate explanation, and here Kant examines the limits of reason and what it can truly know (mostly in regards to free will, the immortality of the soul, or the existence of God). Knowledge, unfortunately, is bound to possible experience. What we can know, what we can reasonably believe, and what we can merely speculate about are different things.

Freedom/free will is a good example. Kant handles it through empirical and intelligible character: empirically, every action has a cause, yet we still hold people responsible, as though their reason could act independently of that chain. He does this without claiming to know freedom beyond experience.

The lesson I'm taking away is a practical one: the strength of an argument isn't the same as knowledge. In the Transcendental Dialectic, Kant shows that reason, left unchecked, can build seemingly airtight arguments for conclusions it has no way of verifying, even proving opposite claims with equal conviction (the world has a beginning in time and it doesn't; we are free and everything is determined). But he doesn't say these ideas are worthless. They work as regulative principles: we can't know them, but they guide inquiry toward a completeness experience never fully gives us. That matters in the age of AI, where llms can build incredibly persuasive arguments on demand. We shouldn't mistake sophistication and confidence for epistemic authority, or hand over our critical judgment just because something, human or machine, sounds like it knows more than we do.

It also leaves me with a question. Though I might be straying from the book's intention here, it came to mind in the last chapters.

Kant says theoretical reason can't establish God or a future life, but practical reason gives them moral weight, since virtue and happiness don't always match in the world. That got me thinking: humans have produced countless competing visions of how the world ought to be, ideals that don't yet exist but shape what we do. Some inspired progress, others justified immense suffering. If reason can conjure so many versions of the highest good, how do we tell the ideal that deserves our allegiance from the one that merely persuades us?