 Now that we've seen that it can be pretty hard or even impossible to establish if something is indeed true, let's ask a different question. How can we know that things aren't true? This type of question was what the philosopher Karl Popper asked. Popper's philosophy builds on the principle of falsification, that means subjecting a claim to a critical test which could refute the claim. Let's go back to our example about royals' balls. We saw the shaky conclusion that all royals' balls are spheres, given individual observations that certain balls are indeed spheres. In a Popperian sense that all royals' balls are spheres is a falsifiable claim because a test to this claim exists that could refute it. We need to search for a non-spherical royal ball to refute the claim that all royals' balls are spheres. If we found one such non-spherical royal ball, the claim that all royals' balls are spheres would be refuted or falsified. Let's try our luck with falsifying some claims. Here's an exercise. Think about how you could falsify these claims. Pause the video to think about this task and resume when you're ready to talk about it. How could you falsify the claim that all frogs are green? Well, you could try to find a non-green frog. In fact, some frogs of different colors exist, such as the remarkable black and blue poison dart frogs. How could we falsify the claim that there is no life outside of Earth's atmosphere? We would need to find life outside of Earth's atmosphere, such as on ISS. Done. And finally, how could we falsify the claim that laughter is the best medicine? Well, we would need to find a case where medication other than laughter is more efficient in treating a disease. You could think of someone suffering from a bacterial infection. Antibiotics will be more probable to cure it than laughter. Now, let's try another exercise. Look at these two claims. Could you falsify them? And if you find it difficult to falsify them, how would you need to reformulate them so that they allow falsification? Let's look at the first claim. To be human is to suffer. This claim might be tricky to falsify because it is quite unclear what suffering means. You will need to take care to stringently define what suffering is. And only then could you turn to aiming to falsify the claim by trying to find a human who has, according to your definition, never suffered. But this example points out that there are claims that are so vague that they are almost impossible to falsify. If someone did not agree with your definition of suffering, they would not think that your critical test was indeed well suited to test their theory, making it hard to refute it. In the second claim, falsification would also be tough. If you wanted to falsify the claim that a sea monster lives in Loch Ness, you could search the lake. However, well, the monster might be hiding or it might be invisible, and then you might not find it. Not to find it that does not falsify the claim that it lives there. You could, however, falsify the claim that the Loch Ness monster does not exist. And you do that by finding it. Now that you know how falsification works, let's see how it can be used in the quest to gain new insight. Remember that we saw before that we can't really prove anything to be right. Then how does one gain new insights? Popper would argue that in any case, you first need a theory, a hypothesis or some speculation of how you think the world works. Then you can try to falsify this theory through putting it to a critical test. If the test refutes your speculations and hypotheses, you need to revise them, and then you can start over. If the critical test is resisted and your theoretical speculation is at least not falsified by this test, then you'd want to revise your ideas for falsifying the theory and make another falsification attempt. Therein, Popper would advocate a research cycle in which you try to consistently understand which parts of your theory aren't true. If you do this diligently, you should in the end be left with only the parts of the theory that cannot be falsified or that resisted all of your falsification attempts. You will never quite know the truth, but you get closer to it by finding out what's not true. Popper called these types of well-tested theories corroborated, but you should still remember that we would even then know not quite that they're true. Basically, Popper argued that the theories we have aim at the truth and that we can approximate the truth with this approach. Finally, let's conclude with an exercise in critical rationalism. Find a hypothesis about the world that you think is interesting. For instance, look up a topic that interests you in a newspaper and see if you can find a falsifiable claim about this topic in it. These claims could be all sorts of statements, such as education relieves poverty or teenage pregnancies are avoided by better education. Then think about how you would critically test this claim. What would be a critical test to falsify it? And given that you do falsify it, how would you revise the hypothesis? Or given that you don't falsify the claim, is there another critical test you could use? Pause the video and return to see an example of how this exercise could be solved. Let's say I read about the claim that eating immediately before going swimming causes an increased risk of drowning. This is a pretty commonly held belief. You will also remember that it's not really possible to look for something, like the effect of eating or risk of drowning, and then conclude it doesn't exist because you don't find it. As in the case of the Loch Ness Monster, you might have just looked in the wrong place. So this means we first have to reformulate a question to make it falsifiable. The falsifiable claim would be that eating before swimming does not actually cause an increased risk of drowning. This is a claim we can falsify if we find that indeed eating before swimming does cause an increased risk of drowning. What a neat little trick. Now, we could put the claim to a critical test by assessing the survival rate of swimmers after eating compared to the survival rate of swimmers who have not eaten for two hours. If this test showed that there was no difference in the survival rates, would this already be enough to revise our theory and assume that eating immediately before swimming does not cause an increased risk of drowning? Probably not. It could be that we just didn't sample from the right people. Maybe people with a heart condition have increased chances of drowning if they swim after eating or children. There would be a lot of other critical tests to run. If these tests all falsified the claim, then we might revise the original hypothesis. Maybe eating food isn't a problem, but drinking alcohol might be. And again, we could think of a new series of tests to falsify this new claim. This concludes this part of the course. Here, we have embraced the idea that if we can't really test what's true, we can at least try to find out what isn't. We use the Popperian scientific method of falsification, which puts claims about the world to critical tests, making it possible to refute them or to uphold them while searching for other critical tests that may indeed then refute them. We have seen that critical rationalism can help us understand the world without relying on the exact truth. Instead, we can try to approximate the truth by continuously asking what is false? In the next part of the course, we will have a look at how to rely on existing theories, paradigms, and research programs.