to put very simply a logic fallacy is a kind of reasoning a pattern of reasoning that will lead you astray in order to avoid these traps of bad reasoning we want to identify common patterns that is why today I'm going to talk about 19 of the common logical fallacies that you might be committing or that you might encounter two quick notes one is that logical fallacies are often hard to determine in practice I'm going to give you easy examples but it takes work to figure out if you are committing a logical fallacy or if your dialectical opponent is also committing one argue with caution I would say and don't accuse people of logical fallacies too often that just doesn't end well and the second point is that you want to study logic there is a fantastic free textbook called for all X it is totally free it is open source you can use it you can change it you just have to follow the Creative Commons license it's all there and there is a link Down Below in the description the most common logical fallacies is the ad hominem and this is the fallacy of attacking the person who is arguing rather than the r argument itself so instead of trying to attack the reasoning or say that the premises are false or that the inferential pattern that they are following is not a valid one you instead start to insult the person call into question their character or their actions the truth is bad people sometimes have correct beliefs and even worse sometimes bad people make good arguments so you want to make sure that you are always focusing on the argument and not the person making it a straw man is when you mischaracterize an argument in order to make it appear weaker than it actually is the opposite of straw Manning is the principle of Charity or recently has been called steel Manning we want to describe our opponent's beliefs in the strongest possible terms so that way when we are able to refute them we know that we've actually been highly successful and we haven't actually just argued against a position that nobody would hold an appeal to Authority is when you appeal to someone's position or expertise in order to establish the truth of a claim now often in ordinary reasoning we do want to rely on Experts experts are by definition often write and usually trustworthy but it is also possible for experts to be wrong and that is why we want to actually look at the arguments and the evidence for claims if you are going to appeal to Authority say as preliminary evidence for the claim make sure you are picking the right experts when you present someone with a false dilemma what you are doing is presenting them two choices as if those were the exhaustive options you'll notice by the way that false dilemmas are often presented in policy decisions or in politics you know the common form of argument in an election is to say well have you seen the other guy he's even worse than me as if there were only ever two options and as if we had to be okay with the fact that there were always two options we had to choose from and equivocation is when you use the same word but with different meanings so consider the argument that's premise one feathers are light premise two what is light cannot be dark and then the conclusion therefore feathers cannot be dark obviously this absurd crows exist there are lots of dark feathers because there are black birds and we know what's gone wrong here we've used light in two different senses and one we're referring to weight and in another we are referring to color but it just so happens that we use the same word in English to describe both of those features you are making a circular argument when you are assuming what is being disputed or what needs to be proved suppose you're in an argument with someone and someone says to you that you should believe the Bible because the Bible is the word of God and then someone says well how do we know that the Bible is the word of God and they say well we know it because it's in the Bible what they have done is appeal to the reliability of the Bible in order to assert that the Bible is reliable that's just a bad form of reasoning by the way that is also called begging the question in some logic textbooks I and every philosopher that I know love the phrase begging the question in this sense but most people say beg the question when they really mean something like raises the question we have just lost that linguistic fight a hasty generalization is just what it says on the tin it is a generalization that you have made with insufficient evidence you've been Hasty when you were generalizing the comparative fallacy is when you make a comparison and then try to establish the absolute claim so I am taller than my wife but that does not mean I'm tall I'm five six I'm not tall comparisons can often be misleading and they have a very tricky role to play in inference go back to our political example that when we talked about false dilemmas just because one candidate is better than the other guy does not mean he is good keep that in mind let's introduce a Latin phrase and that is post-hoc ergo propter Hawk this is the fallacy of attributing causation just because one event precedes another in 1969 a man walked on the Moon it was Neil Armstrong and then in 1973 Richard Nixon was embroiled in the Watergate scandal we should not conclude that because Richard Nixon walked on the moon that Nixon was embroiled in Watergate there are two independent events they are mostly irrelevant to each other establishing a causation is actually a very tricky thing and that is why statisticians like to remind us that correlation is not causation if you claim that something is true just because it hasn't been proven to be false you are making an appeal to ignorance if you claim that just because something is natural it is good you are making an appeal to Nature now some things that are natural are good we could have conversations about that but many things that occur in nature aren't so consider the fact that chimpanzees commit lots of random acts of violence to other chimpanzees or other creatures that doesn't mean that violence because it is natural is good in fact we should aspire to be as non-violent as possible and if you are appealing to popular opinion to establish the truth of a claim you are making an appeal to popularity people often have false beliefs and that does not change when you increase the number of people crowds can often be misled and it turns out that widespread beliefs can be false but by association is when you discredit an idea because it is shared by a group that you deem to be mad or despicable or somehow undesirable this along with ad hominem attacks are two of the most common fallacies that you will see in political advertising the no true Scotsman fallacy is when you revise definitions in an ad hoc fashion in order to avoid counter examples or to avoid some kind of criticism particularly of groups we're very fond of saying well those aren't real members of that group when we don't like those people in particular you'll see this in politics you'll see this in religion you will see it all over the place the fallacy of composition is when you assume that what is true of the parts must be also true of the whole the fallacy of division is when you assume that whatever is true of the whole must be true of the parts and appeal to hypocrisy is when you try to dispute a claim because the person arguing for it fails to act consistently for instance I believe the claim lying is wrong is true but I have lied in my life that does not make the claim false it just means that I have failed to live up to my own ideals appeals to hypocrisy are closely related to ad hominem attacks the burden of proof fallacy is typically described as saying that the weight of evidence lies with the person who's trying to dispute a claim or disprove it rather than the person who is trying to prove it arguments about burden of proof in practice in real life are massively boring and massively frustrating the conversation of the argument will simply go nowhere and then finally my favorite fallacy the fallacy fallacy there are many bad Arguments for good and true conclusions and just because someone makes a bad argument for it does doesn't mean that we now know that the negation has been proved so those are 19 fallacies I hope you got something out of this just a reminder there is a link to that textbook down in the description now go and have really good arguments [Music]