In the last week’s article about deductive and inductive arguments, I mentioned something called Hume’s dilemma. In this article, I discuss it in more detail. Here is a short recap of the main idea – the 18th century Scottish Enlightenment philosopher David Hume presented the scientific (and philosophical) community with a challenge: he claimed that inductive arguments cannot be rationally justified. Since the success of the scientific revolution with the natural sciences leading the way was considered to be based on inductive approach (gathering particular observations to formulate general theories), this was a serious challenge. To put it very bluntly, Hume basically said that rationality of scientific knowledge is overrated. He was referring to what we would now call natural sciences like physics. Here’s what he meant.

During Hume’s time, there was a general agreement about the definition of the scientific approach. Coming from the English philosopher Francis Bacon it was already more than 100 years old when Hume presented his challenge. In short, the ‘new’ scientific method described by Bacon in the 17th century set itself apart from the ‘old’ method of Aristotle (deductive) in that it studied the world around us by first making observations and afterwards coming up with general statements inferred from these observations that are further validated by more observations (inductive method). Therefore, the ‘new’ scientific approach addressed one of the main disadvantages of the ‘old’ approach – trying to infer particular truths about the world from preexisting general principles without giving due consideration to the observations we make in the world (for instance, through our senses). With time, the ‘new’ approach became known as the ‘traditional’ scientific approach. The results of this approach were so good (scientific discoveries demystified and explained the world) that hardly anyone thought of doubting its rational validity. In comes Hume and his problem with induction.

Hume’s dilemma, in a nutshell, is the following: we rely on our experience of observed events to make generalised conclusions about unobserved events based on apparent similarities of these events although we know that inductive reasoning does not guarantee the validity of its conclusions. Here is an example. From my experience, I know that whenever I have eaten my favourite type of bread I felt nourished (experience of observed events). When I go to my usual groceries store tomorrow I will buy this same brand of bread and expect it to nourish me for another 3 days as it did in the past (generalised conclusion about yet unobserved events). My expectation of having the same experience with this brad as I’ve had in the past is based on the fact that it is the same brand of bread that I always buy and it is even the same store where I always buy it (apparent similarities of the observed and unobserved events). It is easy for us to imagine, however, that when I eat this bread next time it might no longer nourish me like it did before. There can be various reasons, for instance, I may develop an allergy, the producer may substitute some ingredients or change the recipe without altering the ‘looks’ of the bread, and so on. We can imagine such scenarios, we understand that our previous experience with some ‘samples’ of this brand of bread does not rationally guarantee the validity of our generalised conclusions and future expectations about this brand of bread. There is no logical argument explaining why the future should resemble the past. Yet, we continue to heavily rely on this inductive reasoning.

Of course, it was not Hume’s aim to put the authority of experience in our everyday lives in question (although, I think it is sometimes worth to spend a few moments on considering this as well). His point was about the use of the inductive method in the natural sciences, trusting it fully to discover the truths of nature. In other words, I can accept some uncertainty and even lack of rational justification in my expectations towards bread but I would find it very disturbing if it turned out that there is no rational justification behind any of our knowledge about the ‘laws of nature’. This is exactly what Hume’s presented problem of induction did – it cast a serious shadow of doubt on the rational justification of the ‘traditional’ scientific method. Let’s return to my bread example again. Hume could ask me to provide support for the truth of my conclusion that my favourite type of bread will continue nourishing me in the future. This would be a valid question because, as we saw, it is easy to imagine a situation where it no longer nourishes me, so my conclusion is not the only possible scenario. How can I respond? Well, I don’t have anything except for my past experience, really (observed events). So that is what I respond – this bread will continue nourishing me in the future because it has done so in the past. And here Hume proves his point. He is not arguing about the bread itself, so it does not matter if it continues to nourish me or not. The point here is that I used my past experience to justify my conclusion that I have based on this same experience. This is not a rational justification because I try to justify something that I derived from experience by using this same experience as an argument.

Hume characterised the situation nicely by saying that we are “going in a circle, and taking that for granted which is the very point in question.” (Hume, 1748)

keep exploring!