In The Criqitue of Pure Reason Immanuel Kant sets out to give a systematic account of the metaphysics that underpins empirical inquiry. Kant was operating in the age of the Enlightenment, at a time when scientists like Isaac Newton and his predecessor Galileo loomed large. Empiricism – study based on observation – was making great strides in the sphere of natural science, but there was an undercurrent of doubt: observation based inquiry opens the door to scepticism about our claims about the world.
In A Treatise On Human Nature Scottish philosopher David Hume argues that empiricism is limited in its objectivity by the fact that experience is always mediated by human perceptual and intellectual faculties. Whenever we observe something, we must examine it through particular senses; eyes that pick up light at particular wavelengths, for example. But our eyes can mislead us (does this image depict a duck, or a rabbit?) and so we can not rely on our senses to give us an accurate representation of the world. Hume also thought that our intellectual ‘senses’ were liable to mislead us: he argues famously of observing a billiard ball table on which he observes a ball move towards and strike a second billiard ball. What he doesn’t see is causation. So how do we account for this?
The empirical philosopher John Locke believed that our senses give us impressions of things in the world, and after having an impression so many times, we come to form an idea – a sort of mental picture – of that thing in our heads. We give names to these things, and they become known as ‘tables’ and ‘chairs’ and so on. Hume believed that we come to experience causation in a similar way: by continually observing a causing b, we form an idea in our heads – ‘causation’ – that we impose on the world. And just as there are no actual ‘tables’ or ‘chairs’ out there in the world (there are only impressions given to us by our senses), there is nothing in a itself that causes b. Moreover, if we were re-assembled to form another sentient being, our experience of tables and chairs and causation could be radically different: therefore anything known by way of empirical inquiry is open to doubt.
Kant wants to argue against this. Part of his project is establishing how reason acts on experience: how is it that our knowledge about the world conforms to the way the world really is, and what must be necessary for this to be the case? One way to answer this question would be to argue that our unique human composition, i.e. our perceptual and intellectual faculties being just so, must be necessary if we are to be able to know what the world is really like. It is incoherent to imagine that we could be re-assembled as another sentient being, because if we were not us then we would not be able to experience anything.
It is also true that when a fails to cause b – when my car refuses to move when I push down on the accelerator, – I would not assume that physical laws have suddenly stopped working, I would assume that something in the external world had gone wrong. In this way, Hume’s sceptical argument – that causation could be other than what it is, or not be at all – is inconsistent with the successes of our everyday functioning in the world. Kant’s aim is to show that what we bring to bear on objects in the world – our perceptual and intellectual faculties – preserve objectivity in a way that is sufficient to close the door on Hume’s scepticism.
*This is a written run-through of a lecture on Kant’s project given at Oxford University, which you can watch here.