In fallacies of reasoning, something is, or is perceived as, deficient in the argument, in the reasoning. This video will talk about fallacies of reasoning where the audience perceives a problem with causality. Now one such problem is the slippery slope. This fallacy happens when a speaker identifies a chain of events, but doesn't prove each individual step. >> Did you see this article in the newspaper? >> The what? >> I just read this on my phone. >> What? >> They're building a new lane on the interstate. >> So what? >> So it's going to ruin the towns. >> [LAUGH] How do you figure? >> Okay, a new lane means more housing. More housing means more congestion. Boom, town's ruined. >> So now each step there was framed as a logical consequence of the previous one but it wasn't shown. It wasn't proven. And it's tough because arguing policy's difficult because we're usually talking about the future. We can't see the future. Now in this case, the speaker needed to show that it's a reasonable assumption to say that an extra lane will lead to increased housing development. Now that can be shown, that can be shown through analogous cases that can be shown through testimony. But in doing so the speaker probably also needed to reduce the size of the claims, right? Destruction of a way of life, that's a little much. You need to dial that back, bud. That's an unnecessarily high argumentative threshold. This causal argument needed smaller claims and bigger proof. But at least in that case there was a clear causal sequence. Now in a post hoc fallacy, the speaker mistakes a chronological sequence of events for a causal one. >> I hate buses. >> Why? >> They make traffic so much worse. >> What makes you say that? >> So we passed that levy two years ago, remember? >> Yeah. >> We put more buses on the roads. >> Mm-hm. >> Ever since then traffic has gotten worse. >> So now in that case the city has grown. More people are on the roads and the transit authority has made more routes available to accommodate the larger population. But many people are still going to drive cars. Now the speaker assumes that since bus routes increased before traffic got noticeably worse, they must be the cause. But there was a different cause driving both more buses and more traffic, and it was increased population. So here in this case the speaker needed to show direct impact, and in fact there's probably a case for buses having a negative impact on traffic. Maybe a dedicated bus lane forces more cars into fewer specifically car lanes. But that's a more specific argument than simply saying that buses make traffic worse. There might be an argument to be made there, but it would need a narrower focus. And certainly it would need to account for bus ridership also reducing the number of drivers on the road. All of this is to say, causality's tricky. Your burden is to explain the steps you're taking and show that they actually do prove causality. Generally I think testimony helps you most here. You can point to other experts that validate your sense of causality. And at the very least you want to be able to show that others share your interpretation of this case. That you're not simply fitting a causal structure onto a collection of loosely related facts. [MUSIC]