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By Richard Hollis (aka Ritchie)

I thought I’d kick off the guest posts with a little philosophical thought experiment (hark, is that the sound of you all clapping your hands in glee?). When I wrote the following, I mean it fairly light-heartedly, but with an eye to the fact that we should perhaps remember we have less reason to be sure of ourselves than we may think.

Despite the insistence of many who champion it, Creationism does not qualify as a scientific theory under any reasonable definition of the term. It makes no testable predictions, invokes a supernatural agent and is supported by no observations of the natural world. But does that really matter? Could the theory of evolution, with all its mountains of empirical evidence, still be as irrational as Creationism?

Perhaps so. To see why, it is necessary to understand the difference between deductive and inductive reasoning. Both are ways of constructing an argument. The conclusions of a deductive argument however, are logically entailed by their premises. The conclusions of an inductive argument are merely supported by them.

Premise 1 – All horses are mammals.
Premise 2 – Mr Kips is a horse.
Conclusion 1 – Mr Kips is a mammal.

This is a deductive argument. The conclusion is logically entailed by the premises. It would be a contradiction to assert that the premises were true, and yet the conclusion was false.

Premise 1 – Horse no.1 is brown.
Premise 2 – Horse no.2 is brown.
Premise 3 – Horse no.3 is brown.
Conclusion 1 – All horses are brown.

This is an inductive argument. Here each premise acts as a single observation which supports the conclusion. Yet it is no contradiction to assert that while the premises are true, the conclusion may be false. Even if we had observed 100,000 horses and all of them were brown, this would still only act as inductive evidence.

Science is based on inductive reasoning. Observations are made, hypotheses are drawn up and tested, then critically challenged and re-tested, all under the assumption that the observations and results of the experiments are the result of static natural laws.

Indeed, it may be argued that inductive reasoning is the foundation for learned behaviour. If we put our hand on an open fire, the sensation will be extremely painful. Even from only one such experience, we will assume that coming into physical contact with fire will always feel the same and will avoid doing it again. Natural selection would punish those who did not learn from earlier mistakes. So it would seem that inductive reasoning is both reasonable and extremely useful for survival.

Yet there is a fundamental problem with inductive reasoning which David Hume outlined in his 1748 book An Enquiry Concerning Human Understanding. In a nutshell his argument states that induction rests on the assumption that natural laws are constant and uniform – and that this assumption is wholly irrational.

Stephen Law, in his book The Philosophy Gym, compares this to an ant sitting on a bedspread:

“The ant can see that its bit of the bedspread is paisley-patterned, So the ant assumes the rest of the bedspread – the bits it can’t see – are paisley-patterned too. But why assume this? The bedspread could just as easily be a patchwork quilt… We are in a similar position to the ant. The universe could also be a huge patchwork with local regularities, such as the ones we have observed – the sun rising every morning, trees growing leaves in the spring, objects falling when released, and so on – but no overall regularity.” (p156)

Such local regularities could have boundaries in time as well as space. Perhaps the natural laws of the universe change suddenly every 100,000 years – and the next change is due tomorrow! What is to say that we will not wake up tomorrow to find the sky is red, or that dropped objects remain suspended in mid air? Note that it is no defense to say, ‘the laws of nature have always stayed constant in the past’, since that is itself a piece of inductive reasoning.

The classic mistake is to misinterpret Hume’s argument. He is not saying that we merely cannot be certain of our inductive conclusions: he is saying that we have no reason at all to believe them. We have no justification for expecting the sky to appear blue rather than red tomorrow. Either is just as rational. And the theory of evolution, based as it is on inductive reasoning, is no more or less rational than Creationism.

In conclusion it seems – according to Hume, at least – that we are always unjustified in drawing conclusions via inductive reasoning. It is as rational to expect a dropped ball to float in mid air as it is to expect it to fall. If you think the first proposition sounds ridiculous compared to the second , then this may tell you far more about human reasoning than it does about logical induction.

But it would be a mistake for Creationists to see Hume’s argument as supporting their ideas. Creationism may be as rational an explanation for the existence of the Earth and life on it as any theory science has yet put forward. But, if so, then so is every other explanation you could possibly make up. To reach a point where Creationism is a rational alternative to the theory of evolution, we have reached a point where the whole of science is meaningless and all certainty we have in any knowledge has been cut loose. We really are as justified in believing in the Flying Spaghetti Monster as we are in believing in God.

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