People will usually accept new information as long as it doesn’t conflict with an emotional belief that’s part of their identity. When this is challenged, they engage in motivated reasoning, defending their belief illogically and dismissing inconvenient facts. It’s triggered by cognitive dissonance, psychological discomfort which occurs when two ideas conflict. It’s human nature, but we can try to avoid it by not getting emotionally attached to factual beliefs that might turn out to be wrong.

When arguing with someone, it’s best to apply the principle of charity and give the other person the benefit of the doubt. Keep in mind that the goal of an argument shouldn’t be to win, but to have the most valid position. This sometimes means changing your own mind. Try not to engage in rationalization, which is starting with the conclusion you want to be true, then reverse-engineering arguments to support the conclusion you want.

There are many informal logical fallacies that get used in arguments such as the argument from authority. This is when you state something is true because an authority figure says it’s true, but this is a fallacy because authorities aren’t always right. For example, Nobel laureate Linus Pauling was a brilliant man, but he was wrong about vitamin C helping fight off infections like the common cold. However, it isn’t an argument from authority to accept the scientific consensus. Evolution, for example, is accepted by 98 percent of scientists, it has mountains of evidence supporting it, and it has withstood numerous attempts to disprove it for over a century. It’s not a fallacy to point this out.

Post hoc ergo propter hoc is the fallacy that because B happened after A, A must have caused B. This is a fallacy because lots of things could have caused B to happen. A is just one of several things that came before. For example, many people think alternative medicine works because they get better after taking it. However, we often recover from illnesses without doing anything at all, so there’s no evidence the alternative medicine actually did anything. It’s just taking credit for what the immune system naturally does.

Just because two things seem to be related, doesn’t mean they actually are. In the 1990s, both religious attendance and drug use were on the rise. If you claimed rising drug use caused a rise in religious attendance, you’d be confusing correlation with causation. Just because two things are correlated doesn’t mean one caused the other. They could have both been caused by a third thing (like social unrest), or they could have just coincidentally both increased at the same time. It’s important to consider all possibilities.

Ad hoc reasoning involves arbitrarily adding new elements to an argument like saying the reason Bigfoot hasn’t been found is because he can teleport or turn invisible. Tu quoque is an attempt to justify something by saying someone else does it too. However, pointing out that someone else did something wrong doesn’t excuse you from doing the same thing. An ad hominen attack is when you attack the person making the argument rather than the argument itself. Even if the person you disagree with is the worst human who ever existed, it doesn’t necessarily mean their argument is wrong.

The argument from ignorance is a logically fallacy which states that a belief is true because we don’t know that it isn’t true. An example of this is the God of the gaps argument. Whenever there’s a gap in scientific knowledge (such as not knowing how the universe first began), some people will say the answer is God did it. But this is a fallacy because if we don’t know something, all we can honestly say is we don’t know something.

A false dichotomy is compressing numerous possibilities into just two. For example, arguing that ghosts exist because someone said they saw one and we know they aren’t a liar. This is a false dichotomy because there’s much more than just two possibilities. The ghost sighting could have been caused by an optical illusion, a false memory, a hallucination, or numerous other possibilities we haven’t thought of.

A false analogy is saying because two things are similar in one way, they must be similar in others. An example of this is saying because both watches and humans are complex, they both must have been created by an intelligence. However, this is a false analogy because watches and humans are different in many ways. A better analogy is comparing evolution to an unplanned city that gets added to in a haphazard way but still works because people change the city to fit their needs. Creationism can be compared to a planned city which was entirely designed from the ground up and thus doesn’t have any haphazard additions being added over time.

The nirvana fallacy is when someone says that if something isn’t perfect, it’s worthless. This is untrue because something can be better than nothing even if it isn’t perfect. The no true Scotsman fallacy changes the definition of a word in order to win an argument. For example, if someone says all Scotsmen are brave and you point out a Scotsman who’s a coward, they’ll say he isn’t a true Scotsman. It’s a form of circular reasoning.

Reductio ad absurdum is when logic is stretched to force an absurd conclusion. The Slippery slope argument is when someone claims accepting a position also entails accepting an extreme of that position, which isn’t necessarily true. A straw man argument is when you argue against a weaker version of your opponent’s argument. You should argue against what they actually said rather than an easier-to-defeat argument. The reverse of this is the steel man in which you argue against a stronger version of their argument in order to be as fair to their position as possible.

The texas sharpshooter fallacy is deciding after the fact what the evidence should have been. Think of someone shooting at the side of a barn, then later going up to the barn and drawing a target around where they hit and claiming they got a bulls-eye. The moving goalpost is arbitrarily changing the criteria for proof when evidence is met, sometimes demanding impossible criteria be met. And, of course, the fallacy fallacy is when you say someone is wrong because they committed a logical fallacy, but this doesn’t necessarily mean that they’re wrong. Their argument could be terrible, but they still might be right.