Critique of Pure Reason
Immanuel Kant
1781 (revised 1787)

Kant’s “First Critique” – before those of Practical Reason and Judgement – is not only his most significant, but one of the most important books in all of western philosophy. A reaction to the rational skepticism of David Hume, Kant’s work seeks to explore and understand knowledge that is independent of experience. We do understand the world through experience, but that isn’t the whole of it.  We also know the world a priori – meaning, in the words of contemporary philosopher Galen Strawson, “you can see that it is true just lying on your couch. You don’t have to get up off your couch and go outside and examine the way things are in the physical world. You don’t have to do any science.”

Consider two propositions – all bodies have mass, and all bodies have weight. In the former instance, the predicate concept (mass) is always-already existing in the subject concept (bodies) – that is, a body always signifies to us something with a mass. In the latter case, the predicate is not necessarily contained in the subject – we don’t know whether a body has weight until we actually experience that weight. The former type of proposition Kant calls analytic – nothing external is needed to make sense of it. The latter type, on the other hand, is synthetic – its meaning is derived from the combination of the subject and something external to it. OK. But this wasn’t anything earth-shattering; philosophers had already made this distinction. But Kant goes a step further. While previous thinkers – and Hume in particular – had derived from the analytic/ synthetic distinction the conclusion that all synthetic propositions require experience, i.e something observable and external to the mind, Kant suggests that some synthetic propositions require no experience – not only are some things true before we learn them, but we can know they are true without any direct experience of them. Some knowledge simply is. How? Because the human mind has the ability to conceptualize and provide order, and sometimes it is only by virtue of that internal and organic intellectual ability that something can be experienced at all. Yes, the external world stimulates our senses and thus provides experience. But it is the mind that perceives and interprets that sensory input and turns it into experience. “Thoughts without content are empty”, he concludes; “intuitions without concepts are blind.”