‘Thoughts without content are empty, intuitions without concepts are blind.’
With this thought, Kant attempts to bring together the apparently opposed ideas of empiricism and rationalism. He synthesises their views in the claim that empiricism was right to say that experience, in the form of sensory perception (intuitions to Kant) is essential to knowledge, but the rationalists were right to say that the mind’s ‘rational’ structures make our understanding of those sensory perceptions possible by imposing the (‘pure intuitions’ of time and space and the ‘categories’ of:
quantity: (unity, plurality and totality);
quality: (reality, negation, limitation);
relation: (inherence and subsistence, causality and dependence, and repriocity):
modality: (possibility and impossibility, existence and nonexistence, and necessity and contingency)
Without these organising structures experience itself would not be possible. We are so built, he thinks, that we have to experience the world outside ourselves as spatial and temporal (flowing through time) not because the outer world is spatial and temporal, but because we impose spatiality and temporality on the 'intuitions' we have of it.
It is in this sense that Kant’s philosophy represents a ‘Copernican turn’, rather than the world somehow imposing understanding of itself on our minds, our minds impose our understanding on the world - our minds give the the world the form we perceive it as having.
However, according to Kant, it is not the actual world 'in itself' that we perceive, this is beyond our perception; what we experience is the world of 'phenomena', the underlying reality behind the world we experience the world of 'noumena' is forever hidden to us.
Kant’s Synthetic a Priori
Kant believed that claims about the world could be both 'synthetic' in that they could tell us something about the world that isn't contained in their own terms, and 'a priori' because they can be known independent of experience of the world.
This is a response to Hume who had denied such a possibility. 'Hume's fork' (see previous entry) made a strict separation between synthetic propositions, which for him could only be known 'a posteriori' and 'analytic' propositions which could be known a priori, but told us nothing about the world that was not already contained in their terms.
To understand this we have to look at the way the sentences we use to make propositions and claims about the world work. Sentences consist of subjects (the thing the sentence is about) and predicates (the words that say something about the subject). So, the sentence ‘Some frogs are green’ has ‘Some frogs’ as its subject and ‘are green’ as its predicate.
Both Kant and Hume thought that 'analytic' statements are those in which the subject contains the predicate and consequently they don't add any information about the world: an example of this would be the sentence ‘green frogs are green’, or to push it a little further, 'kangaroos are animals', because we could claim that the concept of 'kangaroo' contains the concept of 'animal', so if we already have the concept of 'kangaroo' we already have the concept of 'animal' and we know this independent of (further) experience', we know it 'a priori'.
On the other hand the predicates of 'synthetic' statements are not contained in the subject, so they do give us additional information about the world; for example ‘This frog is green’ or 'this kangaroo has a stamp collection.'
But Kant thought that statements like '7 + 5 = 12' were both 'synthetic' and 'a priori', in fact he thought that 'Mathematical judgments are all, without exception, synthetic.' For Kant, there is nothing contained in the concept of '7' and '5' that makes the knowledge that adding them together will result in '12' immediately obvious or ineluctable. What he was getting at is perhaps easier to see if we consider larger numbers like for example, 38976 and 45204; their sum 84180 certainly does leap out at me, but I'm v. poor at maths. I think this gives an inkling of what Kant meant, but an awful lot of reading is really required to work your way into his idea.
Kant also thought that science could come up with synthetic a priori statements. He claimed that the statement, 'In all changes in the physical world the quantity of matter remains unchanged.' was such an example; he said;
Now, in thinking the concept of matter I do not think its permanence but only its presence in the space that it fills. Thinking that matter is permanent isn’t like thinking that women are female, or that tigers are animals. In judging that matter is permanent, therefore, I go beyond the concept of matter in order to add to it something that I didn’t think in it. So the proposition isn’t analytic but synthetic; yet it is thought a priori. He also claimed that the statement, 'When one body collides with another, action and reaction must always be equal' was synthetic and a priori.
Again it is not obvious (not to most mortals anyway) exactly what he meant, but if we consider his ideas about the 'categories': how we experience the world in the way we do because time, space and cause and effect are built in to the way our minds are set up to experience the world, then we begin to see how we might know 'a priori' the stuff above about action and reaction, and such 'knowledge' certainly seems to add to our information about the world and is therefore 'synthetic'. Hume, of course denied that ideas about cause and effect, action and reaction etc. were anything other than the product of experience and as such, although synthetic, could only be known 'a posteriori'.
Causation is another example of synthetic a priori knowledge Kant claims that ‘Every event has a cause’ can be known a priori and is synthetic because it tells you something that isn’t contained in the terms: event is not synonymous with cause - depends how you think about it really!?:/
So, I hope that's clear, now. Another Saturday afternoon bites the dust of metaphysical speculation.