In my own personal discussions with theists, and in those I have observed involving others, one accusation that seems to come up frequently is that atheism presupposes or is biased towards naturalism, and averse to the supernatural. This accusation is made so that the atheist will appear to have made a closed-minded and dogmatic denial of the supernatural based only on their commitment to naturalism. This portrayal is inaccurate and deliberately misleading, and in this post I shall attempt to explain why.
One thing which I do presuppose is the null hypothesis – which is the default position. When testing a treatment for example, the hypothesis would state that ‘this treatment will have an effect’ whereas the null hypothesis would state that ‘this treatment will have no effect’ (an analogous concept would be ‘innocent until proven guilty’). Why should I be justified in presupposing the null hypothesis? Because it’s important to start at the default position and seeing whether that is falsified before drawing conclusions. You assume a defendant is innocent until the evidence presented in the trail falsifies that hypothesis. It would be completely unworkable if you assumed their guilt before seeing the evidence, just as it would be dangerous to assume that a treatment works before testing it.
From this perspective naturalism can be redefined as that which has been shown to falsify the null hypothesis. I don’t presuppose that, I can demonstrate that. Supernaturalism on the other hand has not falsified the null hypothesis – there has not been any evidence put forth to demonstrate that the assumption ‘supernatural phenomena do not occur’ is false. For that reason I maintain the default position. Not out of presupposition or bias, but because there is no good reason not to.