Informal Logic: Introduction to Logical Fallacies
We've just wrapped up a lengthy discussion on formal logic, so I think one of the next natural questions is "Is there an 'informal' logic? What's the difference?"
If you read through the series on formal logic, you may remember clear back in Part 2, that I mentioned that formal logic is primarily concerned with the structure of the argument. For instance:
1. If Max is a Poodle, then Max is a Dog.
2. Max is a Poodle.
3. Therefore, Max is a dog.
If you find yourself in an argument where you are certain that your opponent is incorrect, but are not quite sure why, try to see if you can spot an informal fallacy somewhere that might expose the hole in their reasoning.
Appeal to Tradition (similar to the bandwagon fallacy) - (e.g., astrology, religion, slavery) Just because people practice a tradition, or "It's always been done this way" says nothing about its viability, moral status, or facticity.
Bandwagon Fallacy - Concluding that an idea has merit simply because many people believe it or practice it. (e.g., Most people believe in a god; therefore, it must prove true.) Simply because many people may believe something says nothing about the fact of that something. For example many people during the Black plague believed that demons caused disease. The number of believers say nothing at all about the cause of disease. (Note: Bandwagon Fallacy concerns itself with what people believe now. Appeal to Tradition concerns itself with the beliefs of past people.)
Begging the Question - an argument in which one or more of the premises assume the truth of the conclusion. (e.g., "If left to themselves, children will naturally do the right thing because people are intrinsically good." or "We know that the Bible is divinely inspired because 2 Timothy 3 says 'all scripture is given by divine inspiration of God.'")
Composition Fallacy - Concluding that an item has a characteristic because one or more of its parts does, or concluding that one or more of the parts has a characteristic because the whole item does. (e.g., Humans have consciousness and humans consist of atoms; therefore, atoms have consciousness. Or: Sodium ignites when placed in water and there is sodium in table salt, therefore table salt ignites when placed in water. This is a favorite fallacy among anti-vaccine propagandists who talk about the "chemicals" in vaccines.)
Confirmation Bias - Focusing on evidence that supports what a person already believes (or wishes to believe), while ignoring evidence that refutes that belief. Confirmation bias plays a stronger role when people base their beliefs upon faith, tradition, or prejudice. For example, if someone believes in the power of prayer, the believer will notice the few "answered" prayers while ignoring the majority of unanswered prayers (which would indicate that prayer has no more value than random chance or a placebo effect). Confirmation Bias is also typically at work when people post YouTube videos that cite no sources (or maybe cites one or two "experts" of dubious reputation) while ignoring the vast majority of actual research done (or decrying all other experts and research done on the topic as the work of "shills").
Confusion of Correlation and Causation - As its name suggests, this fallacy occurs when two things appear together and it is thus assumed that one causes the other. A prime example of this is people who claim that fluoride in water leads to Autism, noting that the percentage of people in the U.S. who have been diagnosed with autism has increased dramatically over the last 80 years, as has the percentage of people in the U.S. who have access to fluoridated water. Of course, this ignores that our understanding of autism has also evolved considerably over the past 80 years or so, and the diagnostic criteria have changed quite dramatically, such that many people who would not have been considered autistic had they been assessed in the 1950's are considered autistic by the standards used today.
Post Hoc, Ergo Propter Hoc (Latin for "It happened after, therefore it was caused by.") - As its name suggests, this is the fallacy at work when someone says "I prayed for them, and they recovered for their illness, therefore prayer has healing abilities." or "I wished on a shooting star and then got that promotion I wanted, ergo shooting stars are magic." Just because one thing happened before another does not prove that the former caused the latter.
Red Herring - when the arguer diverts the attention by changing the subject.
Reification Fallacy - treating an abstract belief or hypothetical construct as if it were a concrete, real event or physical entity (e.g.: Saying that evolution selects which traits are passed on to future generations; evolution is not a conscious entity with agency. While the term "selection" is used when discussing evolution, it's important to keep in mind that the use is figurative. Biologists and others knowledgeable in the topic are not intending to state that evolution is an entity that is consciously making these choices).
Russel's Teapot (proving non-existence) - while we have stablished in our series on formal logic that it IS possible to prove a negative, there are some claims that simply do not lend themselves to formal disproving. If someone asks "Can you PROVE that unicorns don't exist? Can you prove that there is no planet anywhere in the universe where unicorns exist?!" the simple answer is "No". Such a task is presently outside of our abilities as a species. However, the simple fact that we cannot prove it false does not provide evidence that it is true. Belief in unicorns remains utterly without any basis in fact.
Slippery Slope - a change in procedure, law, or action, will result in adverse consequences. (e.g., If we allow physician-assisted suicide, then eventually the government will control how we die.) It does not necessarily follow that just because we make changes that a slippery slope will occur. Do note however, that there are also "Slippery Slope Arguments". Sometimes the slope really is slippery, and sometimes actions are likely to have unintended consequences. It's important to be able to discern if a given situation is actually likely to unintended consequences, or if the allegations of adverse consequences are entirely without merit.
Special Pleading - Insisting that an exception to a rule should be applied to a specific case, without proper justification of why that case deserves an exemption. (e.g. appealing to God's "mysterious ways" to get out of providing an explanation for how an all-knowing, all-powerful, and all-good god could allow evil to exist. Or insisting that astrology is real, but you just have to trust them that it works and not ask for explanations as to how it works.)
Straw Man - Creating a false scenario by misrepresenting an opponent's argument in such a way that it is easier to refute and then attacking that weaker version of the position. For instance: "Evolution says everything happens by random chance!", while it is true that evolution maintains that mutations are random, the forces that lead certain traits to be "selected" (or be more likely to be passed on to offspring) are often highly predictable (i.e. traits that allow the individual to more easily procure food, more easily evade predators, and/or be viewed as a more attractive mate). So starting an argument with "Evolution says everything happens by random chance" is creating a strawman to make evolution seem less probable, and avoid having to have a nuanced discussion about how it actually works.
If you read through the series on formal logic, you may remember clear back in Part 2, that I mentioned that formal logic is primarily concerned with the structure of the argument. For instance:
1. If Max is a Poodle, then Max is a Dog.
2. Max is a Poodle.
3. Therefore, Max is a dog.
This argument has the basic structure:
1. If A then B
2. A
3. Therefore B
Because the argument has a valid structure (in other words: It takes a valid "form") it is a valid argument. So formal logic concerns itself with the "form" of the argument. (It has nothing to do with whether or not your argument is wearing a bow tie.)
That said, as was mentioned early on in the discussion of formal logic, formal logic does not concern itself with the truth of the premises. For purposes of formal logic, we simply assume the truth of the premises and work from there. As such:
1. If we have always done it that way, then it is the best way.
2. We have always done it that way.
3. Therefore it is the best way.
Is a perfectly valid argument. It follows the same basic structure as we outlined above. The problem is that the first premise is questionable at best. (How many centuries did we spend thinking that "blood-letting" was a cure for illness?) That is where informal logic comes in. While formal logic concerns itself with the form of the argument, informal logic concerns itself with those instances where the form of the argument is fine, but there's some other issue (typically questionable premises) that is causing our reasoning to go astray. These other issues are known as "informal logical fallacies".
(Do note that finding a fallacy in someone's argument does not necessarily prove that their conclusion is wrong, it only means that their argument does not suffice to prove that their conclusion is right. It's often quite easy to reach good conclusions with bad evidence.)
The following briefly describes some of the most common fallacies. (Although, for the most comprehensive list of fallacies that I've ever been able to find, you can also check out Wikipedia's List of Fallacies).
Appeal to Ignorance (argumentum ad ignorantiam) - using our lack of knowledge about a topic as proof that a specific claim is true. This typically takes the form of "This has never been proven false, therefore it is true" (or vice versa). As an example: "We have no knowledge of aliens, therefore they do not exist." Ignorance about something says nothing about its existence or non-existence. Similarly: "We don't know what biases these scientists may have, therefore we cannot trust their studies!" It is not enough to simply imply that biases might exist or have impacted the work. One needs to actually demonstrate that the scientists actually have these biases and that they actually did influence the study.
Appeal to Ignorance (argumentum ad ignorantiam) - using our lack of knowledge about a topic as proof that a specific claim is true. This typically takes the form of "This has never been proven false, therefore it is true" (or vice versa). As an example: "We have no knowledge of aliens, therefore they do not exist." Ignorance about something says nothing about its existence or non-existence. Similarly: "We don't know what biases these scientists may have, therefore we cannot trust their studies!" It is not enough to simply imply that biases might exist or have impacted the work. One needs to actually demonstrate that the scientists actually have these biases and that they actually did influence the study.
Argument from Omniscience - (e.g., All people believe in something. Everyone knows that.) An arguer would need omniscience to know about everyone's beliefs or disbeliefs or about their knowledge. Beware of words like "all," "everyone," "everything," "absolute."
Appeal to Faith - (e.g., if you have no faith, you cannot learn) if the arguer relies on faith as the bases of his argument, then you can gain little from further discussion. Faith, by definition, relies on a belief that does not rest on logic or evidence.
Appeal to Faith - (e.g., if you have no faith, you cannot learn) if the arguer relies on faith as the bases of his argument, then you can gain little from further discussion. Faith, by definition, relies on a belief that does not rest on logic or evidence.
If someone insists that you need to believe that their claim is true before the explanation will make sense, there's a good chance that that person has a vested interest in their claim being true. It's also likely that they are overlooking holes in their reasoning so that they do not have to have to question their belief.
Appeal to Tradition (similar to the bandwagon fallacy) - (e.g., astrology, religion, slavery) Just because people practice a tradition, or "It's always been done this way" says nothing about its viability, moral status, or facticity.
Bandwagon Fallacy - Concluding that an idea has merit simply because many people believe it or practice it. (e.g., Most people believe in a god; therefore, it must prove true.) Simply because many people may believe something says nothing about the fact of that something. For example many people during the Black plague believed that demons caused disease. The number of believers say nothing at all about the cause of disease. (Note: Bandwagon Fallacy concerns itself with what people believe now. Appeal to Tradition concerns itself with the beliefs of past people.)
Begging the Question - an argument in which one or more of the premises assume the truth of the conclusion. (e.g., "If left to themselves, children will naturally do the right thing because people are intrinsically good." or "We know that the Bible is divinely inspired because 2 Timothy 3 says 'all scripture is given by divine inspiration of God.'")
Sometimes begging the question can be well-hidden by having a premise that is heavily implied, but not stated. In a previous post we showed that the argument "The universe is too improbable to happen by chance, therefore God created it!" is a form of begging the question, as it implies that the universe - as it currently is - was a deity's desired outcome, thereby assuming the existence of the deity (which is the very point in want of proving).
Composition Fallacy - Concluding that an item has a characteristic because one or more of its parts does, or concluding that one or more of the parts has a characteristic because the whole item does. (e.g., Humans have consciousness and humans consist of atoms; therefore, atoms have consciousness. Or: Sodium ignites when placed in water and there is sodium in table salt, therefore table salt ignites when placed in water. This is a favorite fallacy among anti-vaccine propagandists who talk about the "chemicals" in vaccines.)
Confirmation Bias - Focusing on evidence that supports what a person already believes (or wishes to believe), while ignoring evidence that refutes that belief. Confirmation bias plays a stronger role when people base their beliefs upon faith, tradition, or prejudice. For example, if someone believes in the power of prayer, the believer will notice the few "answered" prayers while ignoring the majority of unanswered prayers (which would indicate that prayer has no more value than random chance or a placebo effect). Confirmation Bias is also typically at work when people post YouTube videos that cite no sources (or maybe cites one or two "experts" of dubious reputation) while ignoring the vast majority of actual research done (or decrying all other experts and research done on the topic as the work of "shills").
Confusion of Correlation and Causation - As its name suggests, this fallacy occurs when two things appear together and it is thus assumed that one causes the other. A prime example of this is people who claim that fluoride in water leads to Autism, noting that the percentage of people in the U.S. who have been diagnosed with autism has increased dramatically over the last 80 years, as has the percentage of people in the U.S. who have access to fluoridated water. Of course, this ignores that our understanding of autism has also evolved considerably over the past 80 years or so, and the diagnostic criteria have changed quite dramatically, such that many people who would not have been considered autistic had they been assessed in the 1950's are considered autistic by the standards used today.
Do bear in mind that it is possible that a correlation may be a causal relationship, may be two things that share a common cause, or the correlation may be utterly spurious. Regardless, simply showing two things to be correlated does not prove a causal relationship.
Excluded Middle (or false dichotomy) - Insisting that their are only two possible options (often these are "the extremes", but not always). Many people use Aristotelian either/or logic tending to describe in terms of up/down, black/white, true/false, love/hate, etc. There are some times where there are truly are only two options (e.g. you're either pregnant or you're not. There's not really much room for middle ground there) but many times, a continuum occurs between the extremes that people fail to see. The universe also contains many "maybes".
Loaded Questions - Asking a question in such a way that it presupposes something that has not been proven or accepted by all the people involved and that if answered, indicates an implied agreement. (e.g., if someone asks "Have you stopped beating your wife yet?" regardless of whether you say "yes" or "no", the implication is that you did, at some point, beat your wife.)
Faulty Generalization (similar to confirmation bias) - When conducting research, a major part of many methodologies is sample size. If you only have two participants in your study, it's possible that what you learn is a result of some characteristic of those participants and doesn't actually apply to humanity as a whole. If you have 30,000 participants, on the other hand, the odds are much better that your sample is representative of humanity as a whole. If you flip a coin 10 times, you might conclude that the odds of that coin landing on heads are 70%. If you flip it 500 times, you'll probably conclude that the odds of it landing on heads are right about 50%. In both situations having a large number of data points helps put you closer to the truth of the matter.
Faulty generalization assumes that a small sample is adequate to determine the actual probability. (e.g., My parents smoked all their lives and they never got cancer. Or: I don't care what others say about Yugos, my Yugo has never had a problem.) Simply because someone can point to a few favorable numbers, or a few instances of a thing happening says nothing about the overall probabilities.
Loaded Questions - Asking a question in such a way that it presupposes something that has not been proven or accepted by all the people involved and that if answered, indicates an implied agreement. (e.g., if someone asks "Have you stopped beating your wife yet?" regardless of whether you say "yes" or "no", the implication is that you did, at some point, beat your wife.)
Post Hoc, Ergo Propter Hoc (Latin for "It happened after, therefore it was caused by.") - As its name suggests, this is the fallacy at work when someone says "I prayed for them, and they recovered for their illness, therefore prayer has healing abilities." or "I wished on a shooting star and then got that promotion I wanted, ergo shooting stars are magic." Just because one thing happened before another does not prove that the former caused the latter.
Red Herring - when the arguer diverts the attention by changing the subject.
Reification Fallacy - treating an abstract belief or hypothetical construct as if it were a concrete, real event or physical entity (e.g.: Saying that evolution selects which traits are passed on to future generations; evolution is not a conscious entity with agency. While the term "selection" is used when discussing evolution, it's important to keep in mind that the use is figurative. Biologists and others knowledgeable in the topic are not intending to state that evolution is an entity that is consciously making these choices).
Russel's Teapot (proving non-existence) - while we have stablished in our series on formal logic that it IS possible to prove a negative, there are some claims that simply do not lend themselves to formal disproving. If someone asks "Can you PROVE that unicorns don't exist? Can you prove that there is no planet anywhere in the universe where unicorns exist?!" the simple answer is "No". Such a task is presently outside of our abilities as a species. However, the simple fact that we cannot prove it false does not provide evidence that it is true. Belief in unicorns remains utterly without any basis in fact.
Slippery Slope - a change in procedure, law, or action, will result in adverse consequences. (e.g., If we allow physician-assisted suicide, then eventually the government will control how we die.) It does not necessarily follow that just because we make changes that a slippery slope will occur. Do note however, that there are also "Slippery Slope Arguments". Sometimes the slope really is slippery, and sometimes actions are likely to have unintended consequences. It's important to be able to discern if a given situation is actually likely to unintended consequences, or if the allegations of adverse consequences are entirely without merit.
Special Pleading - Insisting that an exception to a rule should be applied to a specific case, without proper justification of why that case deserves an exemption. (e.g. appealing to God's "mysterious ways" to get out of providing an explanation for how an all-knowing, all-powerful, and all-good god could allow evil to exist. Or insisting that astrology is real, but you just have to trust them that it works and not ask for explanations as to how it works.)
Straw Man - Creating a false scenario by misrepresenting an opponent's argument in such a way that it is easier to refute and then attacking that weaker version of the position. For instance: "Evolution says everything happens by random chance!", while it is true that evolution maintains that mutations are random, the forces that lead certain traits to be "selected" (or be more likely to be passed on to offspring) are often highly predictable (i.e. traits that allow the individual to more easily procure food, more easily evade predators, and/or be viewed as a more attractive mate). So starting an argument with "Evolution says everything happens by random chance" is creating a strawman to make evolution seem less probable, and avoid having to have a nuanced discussion about how it actually works.
As stated at the beginning of the post, there are many other informal logical fallacies, but these are some of the most common. Being on the lookout for informal fallacies in your own arguments can help you avoid making poor arguments, and can help you locate the flaws in others arguments as well.
Comments
Post a Comment