In this module, we're going to be exploring some foundational questions about the nature of skepticism. We begin with an important distinction between a healthy skepticism, the antidote to gullibility, and a skepticism that comes in a more radical guidance. We'll consider how the latter can lead to relativism about truth, the idea that there is no objective truth but only subjective viewpoints. As we will see such relativisms in GBS intellectual pedigree, I can also have some pernicious social consequences. Finally, since skepticism purports to show that we know much less than we think we know, we will reflect on the nature of knowledge. Skepticism is about doubt. We often adopt a skeptical attitude and rightly so, as a certain degree of skepticism is usually a good thing. Skepticism in this sense is the antidote to gullibility, and surely no one wants to be gullible. But a healthy moderate skepticism can also easily drift into something more extreme; radical skepticism. Consider for example the skepticism that one finds in certain quarters about the reliability of scientific expertise, such as regarding the scientific consensus or man-made climate change. Notice how this kind of skepticism is very different from being skeptical about, say, what a used car salesman is selling telling you. In the latter case, your doubt is local, and that it is specific to this particular scenario. But when he's doubtful about scientific expertise in general, then one's doubt is no longer local in the sense. If even the scientific experts are not to be trusted, then on what can we rely? A radical skeptical doubt is this endangered cooling everything that one believes into question. Once radical skepticism takes root in our public life, that it has all kinds of practical ramifications, many of them not particularly appealing. One consequence is a lack of concern for accuracy and the truth. Think, for example, of such contemporary phenomena as false facts and post truth politics, whereby people in public life at a manifest file suits seemingly with impunity. A radical skepticism effectively licences such phenomenon. Since everything is up to doubt, then there is nothing that is accepted as true, and hence what's true starts to drop out of the equation altogether. This is why a radical skeptical doubt often gives way to prevailing relativism about truth, whereby the truth is just simply whatever someone says it is. So, one camp endorses the scientific consensus about man-made climate change, whereas another camp argues that the scientists are all part of a global conspiracy to deceive the public. According to relativism, both camps can be right, since truth is just relative to one's subjective opinion. It might initially seem liberating to shake off a concern for truth and accuracy in this way, and to allow that opposing groups can both be right. But this isn't illusion. This is because saying that the opposing camps are both right is as empty as saying that they are both wrong. Once you abandon the idea of accuracy, that is a matter anymore what's true and what isn't. But getting things right should matter to us. The radical skepticism has pernicious consequences, such as leading to relativism does not in itself demonstrate as anything illegitimate about. So what grounds are there for resisting the transition from a healthy moderate skepticism to a problematic radical skepticism.