Hume famously argued that causality was a mental construct and not an objective feature of reality – we see one billiard ball hit another, but we don’t see or sense causation – we merely see the fact of the balls collision and draw the causal connection ourselves. Causes do not necessitate their effects. In theory any effect may follow from any cause.
Chesterton, in his book ‘Orthodoxy’, (specifically, ‘The Ethics of Elfland), pursued a somewhat similar line of thought, though it may be that he was far more radical. Chesterton conceded that there are, in fact, things such as logical and mathematical necessities – one plus one is two, if I am the son of a miller, than a miller is my father. These are necessarily true. But then he makes what may turn out to be a stunning observation:
‘If Jack is the son of a miller, a miller is the father of Jack. Cold reason decrees it from her awful throne: and we in fairyland submit. If the three brothers all ride horses, there are six animals and eighteen legs involved: that is true rationalism, and fairyland is full of it. But as I put my head over the hedge of the elves and began to take notice of the natural world, I observed an extraordinary thing. I observed that learned men in spectacles were talking of the actual things that happened — dawn and death and so on — as if they were rational and inevitable. They talked as if the fact that trees bear fruit were just as necessary as the fact that two and one trees make three. But it is not.’
What Chesterton does here is to note that there is nothing necessary about an actual fact – that X happens does not mean that X is necessary. In all actuality, Chesterton says that anything may happen. There is not a chain of absolute causality about simple factual happenings – in the physical sciences, ‘there are no laws, only weird repetitions.’
Hume took the insight and argued that we have no right to expect that something, say, eating bread, will produce the same effects as it did in the past. I was nourished by bread in the past – but it does not follow necessarily that I will be nourished by it in the future.
Chesterton took this basic point and agreed with it – I’m not nourished by bread by necessity. It’s entirely possible that bread will not nourish me in the future. But what Chesterton argued is that though everything is contingent that happens, and we can’t count on repetition in a logical and necessary sense, reality is structured such that it should turn out to be an odd surprise if one should find trees bearing tigers instead of fruit. Every event is radically contingent, but reality itself is not structured in such a way that anything does come anything. The relations between necessary and logical propositions and facts do not give us a structure of reality as a whole which involves a chain of causation for every event – no event had to occur a certain way.
‘Chesterton’s stunning insistence in ‘The Ethics of Elfland,’ that science as such gives only logical identities and relations but no realities, should make him appear an interpreter of science to be ranked with a Duhem and a Meyerson.’ (Stanley Jaki,‘Interpreter of Science,’ from ‘Chesterton, A Seer of Science’).
It took me a long time to see the force behind Chesterton’s line of thought. The radical contingency and opposition to strict causal laws goes far beyond Hume, in my opinion.