We humans are not rational creatures, we are often wrong. Sometimes we are wrong because we operate on inaccurate data or models, maybe we were forced by time to quickly make a decision. But often we are wrong because of cognitive biases, heuristics build into our brains from the past which might have been useful in the ancestral environment. These are systematic ways in which humans are irrational.
It is important to be aware of these logical fallacies people use in order to effectively call them out and improve the quality of debates. We need to protect ourselves from companies exploiting these loopholes to manipulate us when it comes to marketing and sales. We need to learn how to debias or correct for these biases so as to make the justice system fairer, policy makers smarter and overall improve the quality of decisions individuals make.
Before we fix ourselves, we need to clearly identify the problem. Let me list down some common logical fallacies, heuristics and other cognitive biases you would have seen around you.
We have developed a subconscious processing where we don't bother going on an extensive search of information, we extrapolate from what information we have. We let nearby abstractions leak properties. We call this intuition or gut feeling. In social psychology this is called Halo effect, if you see a person is good looking, we automatically assume without any real evidence that he is also intelligent, kind, honest, etc. If a celebrity is good at sports or acting, we automatically listen to them for political advice and even vote for them since in our heads their compentence in domain carries over to many other domains.
When you are talking about what a group of people, say feminists, communists, or muslims does, you hear people will often say "They are not real feminists". The defense that "true" members of the community don't stand for that, read the actual holy book and note how this behaviour flies in the face of the orthodoxy etc. But practically they are the real life examples of people from that group, words on books don't define the group but the actions of that group matter. This fallacy depends on the fallacy of equivocation since everyone has to agree how to identify a member of that group.
Often when conservatives want to shame people, or make a moral point they will draw on the natural arguments - "Being gay is unnatural", "Ayurveda is natural", "There are natural differences between men and women", "Eating other animals is natural!".
Here we can try to explain how homosexuality is common in the animal kingdom, how heavy metals in Ayurveda medicine is not natural, etc. But there is a fundamental error that people rarely call out and that is this assumption that what is natural is necessarily moral. It is natural to resort to violence when we want to handle conflict and it is natural to commit infidelity, there are many barbaric behaviours that are natural but we civilized ourself and decided it was wrong to have slaves, to restrict individual freedoms, etc.
Even if nature intended it that way due to centuries of evolution, we don't have to do it that way anymore. We can try more efficient solutions instead of sticking with that method we found by trial and error with random mutations.
If you talk about the historical failure of communism, the examples of real dangers it had brought and the potential for harm. Their supporters will often retort - "What about all the issues capitalists have?". If you try to brings up men's issues, people might try to respond with female issues in order to derail the conversation and make it a competition. It is like that quote - "Those who live in glass houses should not throw stones".
People who use this fallacy refuse to engage with the point directly. If someone tries to tell you to quit smoking you point out that he is struggling with losing weight, unless the person is perfect he is not allowed to criticize you. If you try to argue the CCP has flaws they will say America has these other flaws.
5) Straw man
When you are trying to argue with someone, you might see them take your words and then attack an exaggerated version of your point. They can misrepresent your idea, oversimplify it, present it out of context and make it easy to refute.
If you claim women should be allowed to wear what they want and should not be shamed for showing skin, someone might try to say "So you think nude beaches are ok? can they wear bikinis in public places?". They argue in bad faith and act like you hold an extreme version of your actual views. They are just trying to win the debate and not really trying to reach a consensus.
The opposite side of this is steelmanning which I think every person who debates should know about and engage in. When you try to understand your opponent's viewpoint and then improve his argument, and then attack the best possible version of your opponent's argument.
6) Optimism bias
As we live life we need to take risks, it hurts your motivation if you look realistically at the possibilities. It helps your sanity if you are an optimist rather than a realist. So humans have this bias where we underestimate the risk of negative consequences, we also overestimate the probability of success but not as much. People think they are special and especially smart, that others get cancer, get into car accidents, etc.
This bias holds people back from taking risk factors seriously, getting fit, eating healthy, using sunscreen, etc.
7) Cherry picking
People don't always do it on purpose, they are motivated to search out evidence to support their existing position - confirmation bias. Sometimes this manifests as relying only on anecdotal evidence. But it is even worse when they know there is relevant evidence but only present the data that helps prove their point.
8) Appeal to false authority
If you want to use evidence, you can rely on meta-analysis written by subject experts published in top journals. You can rely on the studies rather than just the unsupported claims of an expert. If an expert makes some claims, he needs to cite sources and explain his logic. An expert saying it does not make it automatically true, science has a long history of "experts" being wrong.
There are also cases of false authority, relying on the views of a celebrity on politics, physicists on politics, etc. Ethos is popular way to convince people but it important to accept or reject an argument based on the speaker, you should take it into consideration but it is often overvalued.
9) False equivalence
Analogies are useful to explain ideas, but you have to pick the right analogies. Wrong comparisons can be due to the difference in the magnitude of effect. The equivalence could be based on an oversimplification, ignoring the fact that the two things are actually different. Just because watches and buildings are created by an intelligent mind does not mean the universe also neccessarily has a creator.
10) Ad Hominem
This is a very common attack seen in public discourse. When people are unable to refute the argument the opponent makes on its own merit, they resort to attacking the opponent's character. This makes use of the halo effect, people are less likely to take a murder's argument seriously. By pointing out the speaker has some undesirable trait(s) they manage to avoid having to address the central point.
Some of you may have heard "if all you have is a hammer, everything looks like a nail", an expert in gender studies see the patriarchy as the cause of all problems, an engineering graduate might try engineering solutions to all problems they face.
It is important to recognize the kind of tool you are familiar with and whether that biases you towards or against certain solutions or framing of the problem.
12) False dichotomy
People limit the possible options and present two options acting as if one of the two have to be true. This oversimplifies the choice and excludes nuanced alternatives.
"Since you don't support capitalism, you are a communist", It is possible to be for neither.
"Is gender due to Nurture or Nature?", Talent, gender identity, personality are all determined by a complex interaction of genetics and upbringing/socialization. It is a useful distinction but these two categories are not enough to represent all possible views on the topic.
This sort of a black and white thinking is gaining more popularity because it is hard to disseminate nuanced stances on issues while short crisp ideas like "Abortion is murder of a baby" can go viral.
Many times you will see people who believe in karma, they encourage themselves and others to do good by making the argument that the world is just and someone else will help them when they are in need. This idea has a dark side where victims of crime and misforture are shamed and told that they deserve the suffering they face.
Often people make an argument which you neatly dismantle and show to be false. But they rarely admit your victory, rather they change their position to sidestep your refutation. This can happen multiple times as the person patches their theory on the fly to suit any rebuttal you might have.
15) False Premise
We are polite most of the time and when people use words, we are kind enough to assume it means something real. We try our best to take a charitable interpretation. But this leads to a common fallacy where people take something controversial and nest it in a question as a premise. We are not used to calling out the incorrect premise in people's questions. We should practice listening carefully and point out if any premise used is incorrectly assumed to be true/exist.