I was going to post the second “Thinkbox” today but I noticed that this might be more important. So I will list logical fallacies that most people fall into all the time. It is really important that these fallacies don’t cloud your mind when you try to make accurate deductions. If you, the reader notice that you may be a victim of any of these fallacies try to change your way of thinking.
- Anecdotal fallacy - To use personal experience as proof instead of statistics.
Example: “All women have long hair” because I’ve only met women with long hair.
A way to avoid: Realize that personal experience isn’t as accurate as statistics that have been done on many more people than you can meet.
- Appeal to probability - To think that because something is probable it’s also always the case.
Example: “You must be right handed” because most people are.
A way to avoid: The probability of something does never grantee you that it is correct.
- Conjunction fallacy - Assumption that an outcome simultaneously satisfying multiple conditions is more probable than an outcome satisfying a single one of them.
Example: “Linda is 31 years old, single, outspoken, and very bright. She majored in philosophy. As a student, she was deeply concerned with issues of discrimination and social justice, and also participated in anti-nuclear demonstrations.
Which is more probable?
1. Linda is a bank teller.
2. Linda is a bank teller and is active in the feminist movement.”
Most people chose 2. But the probability of the two occurring together is less or equal to the probability of them occurring alone.
Pr(Linda is a bank teller) = 0.05
Pr(Linda is a feminist) = 0.95
Pr(Linda is a bank teller and a feminist) = 0.05 x 0.95 = 0.0475.
So the probability of her being both are lower than the lowest.
A way to avoid: Just because something seems to fit well together doesn’t mean it does. Try to think critically.
Informal logical fallacies
- Argumentum ad lapidem - Dismissing a claim as false without proof of its absurdity.
Example: “A: Atoms does not exist.
B: Why do you say that?
A: It’s ridiculous.”
A way to avoid: Don’t dismiss anything at first until you have researched the subject you think may be false.
- Argumentum ad ignorantiam - Assuming that a claim is true because it hasn’t been disproven.
Example: “A: Spirits exist.
B: No.
A: Prove that they aren’t real.”
A way to avoid: Don’t think that a hypothesis you have come up it true just because someone else can’t prove it wrong. Extraordinary claims require exceptional proof.
- Divine fallacy - You can’t imagine it to be true so it must be false.
Example: “A: Murder only happen in films
B: Why do you think that?
A: I can’t imagine anyone doing something so wrong.”
A way to avoid: Stop thinking that improbable is the same as false. Like the great Sherlock Holmes once said “When you have eliminated the impossible, whatever remains, however improbable, must be the truth”.
- Argumentum ad nauseam, argumentum ad infinitum - A topic has been discussed so much that is is seen as true or people don’t care anymore.
Example: “You have the left thumb over your right when your fingers are intervened. That means that you are right handed.”
A way to avoid: Stop accepting statements as true, conduct som research. Even if it’s on a small scale it might give you som pointers.
- Argumentum ex silentio - Conclusion is based on the absence of evidence instead of proper evidence.
Example: “A: Ah you are quiet so you did kill him.
B: But I didn’t say anything?
A: That’s why I know!”
A way to avoid: Try not to assume anything without evidence.
- Argumentum ad hominem - To attack a person instead of their argument.
Example: “A: I like ice cream.
B: Well you’re stupid.”
A way to avoid: You likely know that you’re doing this to some extent, so try to be a good debater and come up with a good counter argument. Or maybe just try to understand the other persons point of view.
- Onus probandi - To make a claim and think that other people must accept it or disprove it themselves.
Example: “A: Dogs always lick their owner when greeting them.
B: Not always.
A: Prove that they don’t.”
A way to avoid: Always try to prove your claims, it is your responsibility.
- Circulus in demonstrando - When you begin with the conclusion you’ll end up with.
Example: “A: I think he is right handed.
B: Why?
A: Emm.. Maybe because he has his watch on the left arm?
B: That doesn’t necessarily mean that.
A: It must mean that!”
A way to avoid: Try to observe first and make a conclusion based on the facts. Like Sherlock said “It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts”.
- Post hoc ergo propter hoc - Assumption that correlation is the same as causation.
Example: “He had an heart attack when riding a roller coaster, so that means I will have one on the roller coaster too.”
A way to avoid: Think about the problem you have, does the correlation really equals causation?
- Fallacy of composition - To assume that the whole is true because a part of it is true.
Example: “All cells are aquatic. Therefore all organisms (which are composed of cells) are aquatic.”
A way to avoid: Like earlier, try to be critical and don’t accept something as true without research.
- Black or white fallacy - Two statements are held to be the only possible option, when in reality there is more.
Example: “The coin can only land heads up or tails up”.
A way to avoid: If you are used to problem solving this shouldn’t be to much of a problem. Try to keep an open mind when solving a problem.
- Fallacy of the single cause - Assumption that there is one simple cause of an outcome when in reality it may have been caused by multiple events.
Example: “She has a fear of spiders because she had one in her hair when she was young” When it may have been more that contributed to the phobia.
A way to avoid: Don’t assume that everything is caused by one event, try seeing the whole picture.
- Psychologist’s fallacy - Presumes you can be objective in your judgement.
Example: “A: Something will happen to you if you go out this late.
B: You only say that because I’m your daughter.”
A way to avoid: This is something that is hard to avoid, we as humans will always be biased when it comes to things we care about, so try breathing and think calmly about the problem you wish to solve if you can’t ignore it.
Even though you know these fallacies they will still affect you. No human can get rid of them all, “errare humanum est” (to err is human). But being aware of them hopefully helps you think about the problem you face a bit more.
The ones you should be most aware of is:
Anecdotal fallacy.
This I see all the time. People think that their own experiences must be what everybody else is experiencing too. This is a problem when reading studies and the results of the studies doesn’t correlate with your own experience, so you don’t believe it as much.
Appeal to probability.
Something that people new to deduction often seem to think is that it’s always foolproof. That even though most things in deduction is statistically based it must come true all the time. This isn’t the case, and new people discard deduction as something they cannot learn or something that is false and that’s tragic.
Argumentum ad lapidem.
If you as a deductionist disregard a fact as false without proper evidence you may have trouble learning the art of deduction. Being critical is good but to disregard it entirely isn’t.
Argumentum ad ignorantiam.
Likewise assuming that a fact is true because it can’t be disproven seems to be a trend in the world of deduction. I am still baffled by how many people think that long fingers is connected to piano playing (it’s the fingers flexibility that is connected to it.)
Divine fallacy.
This falls into the same category as the two above.
Onus probandi.
If you have come up with something then it’s also your responsibility to prove it to be right, if you care about it being proven to be correct.
Circulus in demonstrando.
My students in deduction have all done this mistake at least one time each. Try to observe then make deductions.
Post hoc ergo propter hoc.
Correlation does not equal causation.
Fallacy of composition.
If a deductionist have some parts of deduction figured out, well that doesn’t mean they know everything.
Black or white fallacy.
Most of the time it exists more than two options, your job as a deductionist is to figure out which of the options is more likely.
Psychologist’s fallacy.
Don’t ever believe yourself to be completely objective.
And with that, I’ll see you my irregulars.
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