20 Common Logical Fallacies

What is a logical fallacy?
All arguments have the same basic structure: A therefore B. They begin with one or more premises (A), which is a fact or assumption upon which the argument is based. They then apply a logical principle (therefore) to arrive at a conclusion (B). An example of a logical principle is that of equivalence. For example, if you begin with the premises that A=B and B=C, you can apply the logical principle of equivalence to conclude that A=C. A logical fallacy is a false or incorrect logical principle. An argument that is based upon a logical fallacy is therefore not valid. It is important to note that if the logic of an argument is valid then the conclusion must also be valid, which means that if the premises are all true then the conclusion must also be true. Valid logic applied to one or more false premises, however, leads to an invalid argument. Also, if an argument is not valid the conclusion may, by chance, still be true.
Top 20 Logical Fallacies (in alphabetical order)
1. Ad hominem An ad hominem argument is any that attempts to counter anothers claims or conclusions by attacking the person, rather than addressing the argument itself. True believers will often commit this fallacy by countering the arguments of skeptics by stating that skeptics are closed minded. Skeptics, on the other hand, may fall into the trap of dismissing the claims of UFO believers, for example, by stating that people who believe in UFO’s are crazy or stupid.
2. Ad ignorantiam The argument from ignorance basically states that a specific belief is true because we don’t know that it isn’t true. Defenders of extrasensory perception, for example, will often overemphasize how much we do not know about the human brain. UFO proponents will often argue that an object sighted in the sky is unknown, and therefore it is an alien spacecraft.
3. Argument from authority Stating that a claim is true because a person or group of perceived authority says it is true. Often this argument is implied by emphasizing the many years of experience, or the formal degrees held by the individual making a specific claim. It is reasonable to give more credence to the claims of those with the proper background, education, and credentials, or to be suspicious of the claims of someone making authoritative statements in an area for which they cannot demonstrate expertise. But the truth of a claim should ultimately rest on logic and evidence, not the authority of the person promoting it.
4. Argument from final Consequences Such arguments (also called teleological) are based on a reversal of cause and effect, because they argue that something is caused by the ultimate effect that it has, or purpose that is serves. For example: God must exist, because otherwise life would have no meaning.
5. Argument from Personal Incredulity I cannot explain or understand this, therefore it cannot be true. Creationists are fond of arguing that they cannot imagine the complexity of life resulting from blind evolution, but that does not mean life did not evolve.
6. Confusing association with causation This is similar to the post-hoc fallacy in that it assumes cause and effect for two variables simply because they are correlated, although the relationship here is not strictly that of one variable following the other in time. This fallacy is often used to give a statistical correlation a causal interpretation. For example, during the 1990’s both religious attendance and illegal drug use have been on the rise. It would be a fallacy to conclude that therefore, religious attendance causes illegal drug use. It is also possible that drug use leads to an increase in religious attendance, or that both drug use and religious attendance are increased by a third variable, such as an increase in societal unrest. It is also possible that both variables are independent of one another, and it is mere coincidence that they are both increasing at the same time. A corollary to this is the invocation of this logical fallacy to argue that an association does not represent causation, rather it is more accurate to say that correlation does not necessarily mean causation, but it can. Also, multiple independent correlations can point reliably to a causation, and is a reasonable line of argument.
7. Confusing currently unexplained with unexplainable Because we do not currently have an adequate explanation for a phenomenon does not mean that it is forever unexplainable, or that it therefore defies the laws of nature or requires a paranormal explanation. An example of this is the “God of the Gapsâ” strategy of creationists that whatever we cannot currently explain is unexplainable and was therefore an act of god.
8. False Continuum The idea that because there is no definitive demarcation line between two extremes, that the distinction between the extremes is not real or meaningful: There is a fuzzy line between cults and religion, therefore they are really the same thing.
9. False Dichotomy Arbitrarily reducing a set of many possibilities to only two. For example, evolution is not possible, therefore we must have been created (assumes these are the only two possibilities). This fallacy can also be used to oversimplify a continuum of variation to two black and white choices. For example, science and pseudoscience are not two discrete entities, but rather the methods and claims of all those who attempt to explain reality fall along a continuum from one extreme to the other.
10. Inconsistency Applying criteria or rules to one belief, claim, argument, or position but not to others. For example, some consumer advocates argue that we need stronger regulation of prescription drugs to ensure their safety and effectiveness, but at the same time argue that medicinal herbs should be sold with no regulation for either safety or effectiveness.
11. The Moving Goalpost A method of denial arbitrarily moving the criteria for “proof” or acceptance out of range of whatever evidence currently exists.
12. Non-Sequitur In Latin this term translates to “doesn’t follow”. This refers to an argument in which the conclusion does not necessarily follow from the premises. In other words, a logical connection is implied where none exists.
13. Post-hoc ergo propter hoc This fallacy follows the basic format of: A preceded B, therefore A caused B, and therefore assumes cause and effect for two events just because they are temporally related (the latin translates to “after this, therefore because of this”).
14. Reductio ad absurdum In formal logic, the reductio ad absurdum is a legitimate argument. It follows the form that if the premises are assumed to be true it necessarily leads to an absurd (false) conclusion and therefore one or more premises must be false. The term is now often used to refer to the abuse of this style of argument, by stretching the logic in order to force an absurd conclusion. For example a UFO enthusiast once argued that if I am skeptical about the existence of alien visitors, I must also be skeptical of the existence of the Great Wall of China, since I have not personally seen either. This is a false reductio ad absurdum because he is ignoring evidence other than personal eyewitness evidence, and also logical inference. In short, being skeptical of UFO’s does not require rejecting the existence of the Great Wall.
15. Slippery Slope This logical fallacy is the argument that a position is not consistent or tenable because accepting the position means that the extreme of the position must also be accepted. But moderate positions do not necessarily lead down the slippery slope to the extreme.
16. Straw Man Arguing against a position which you create specifically to be easy to argue against, rather than the position actually held by those who oppose your point of view.
17. Special pleading, or ad-hoc reasoning This is a subtle fallacy which is often difficult to recognize. In essence, it is the arbitrary introduction of new elements into an argument in order to fix them so that they appear valid. A good example of this is the ad-hoc dismissal of negative test results. For example, one might point out that ESP has never been demonstrated under adequate test conditions, therefore ESP is not a genuine phenomenon. Defenders of ESP have attempted to counter this argument by introducing the arbitrary premise that ESP does not work in the presence of skeptics. This fallacy is often taken to ridiculous extremes, and more and more bizarre ad hoc elements are added to explain experimental failures or logical inconsistencies.
18. Tautology A tautology is an argument that utilizes circular reasoning, which means that the conclusion is also its own premise. The structure of such arguments is A=B therefore A=B, although the premise and conclusion might be formulated differently so it is not immediately apparent as such. For example, saying that therapeutic touch works because it manipulates the life force is a tautology because the definition of therapeutic touch is the alleged manipulation (without touching) of the life force.
19. Tu quoque Literally, you too. This is an attempt to justify wrong action because someone else also does it. “My evidence may be invalid, but so is yours.”
20. Unstated Major Premise This fallacy occurs when one makes an argument which assumes a premise which is not explicitly stated. For example, arguing that we should label food products with their cholesterol content because Americans have high cholesterol assumes that: 1) cholesterol in food causes high serum cholesterol; 2) labeling will reduce consumption of cholesterol; and 3) that having a high serum cholesterol is unhealthy. This fallacy is also sometimes called begging the question.
Credit to: The Skeptics’ Guide To The Universe

28 responses to “20 Common Logical Fallacies

  1. 21. Argumentum ad populum or the consensus argument. “If everyone believes it then it must be true.” Liberals like to use this one all the time. They combine this with the authority argument to promote Darwinian evolution as something more than a low-grade hypothesis (still lacking any hard evidence of course).

    Essentially, every liberal argument contains at least one of these fallacies. This is because they make it up as they go along to support whatever narrative they’re pushing at the moment. Liberalism has absolutely nothing to do with truth, but with opinion based on feeling and emotion.

    Liberalism is a movent promoting any means necessary to be free from the truth. And truth is that which corresponds to reality.

    • What do you actually know about Evolution? Seems like you know very little, if your claim is that there is little to no evidence for it.

  2. Re your fallacy #3.
    Perhaps my favourite quote is this:
    “Proper science is based not on authority, but solely on reason and evidence” Walter Starck, “‘Threats’ to the Great Barrier Reef”

    It’s a great pity that alarmists don’t heed what Starck has to say from his platform of long and intimate experience with the ‘natural world’.

  3. Spot on with this write-up, I truly feel this
    website needs a lot more attention. I’ll probably be back again to read through more, thanks for the info!

  4. Very insightful. I found this quite interesting, and I’ll have to begin using it in my philosophical studies.

    I would like to point out, though that there is a fallacy in your spelling of the title. Ironic. I wonder why nobody seems to have noticed.

  5. Nice Angela, or is it Michael? Good to see a concise list of commonly used logical fallacies. This should be taught in schools from grade 10! I’m convinced we’d have a better world as a result.

    • Thanks Deon, I agree, we should all be learning these fallacies in school!
      And, I’m Angela (The “About Me” section should give it away)

      😉

    • Thank you for the compliments Keith 🙂
      That Johns Hopkins e-mail was one of the first I debunked. It is still on this site.

  6. Wow! Awesome! Thanks Angela for Valiantly championing truth. Now Warmics, not sure where you get the idea that Scientific theory’s are fact. That’s why they’re called Theories. Gee is there a logical fallacy for conjoining contradictory terms? Theories are, and always will be the short way of saying “Science’s best guess at reality with the information we know which comes from experimented hypotheses whose results we can reproduce”. For a great treatise on the problems of assuming please locate the article by Michael Crichton called “Aliens Cause Global Warming”, please pay special attention to Consensus science.

    Anyway, I don’t know why so many people have such difficulty with the Religion and Science picture. I contend they are not mutually exclusive. Yes the Bible talks about amazing things that we “Can’t understand”, ergo some believe in God. But who’s to say God hasn’t figured out amazing technology that allows him such power? Who’s to say that God doesn’t work through evolution to create the diversity of life we know? Or that we are indeed learning, through science, to act the very way God does? Furthermore (and this is to believers of God) who is to say God doesn’t want us to know how the world works, or to share in the very knowledge that makes him who He is?

    That said, Theologians will never prove the existence of God, and Science will never prove his non-existence, nor do I believe true followers of science or religion are attempting to do so. So let’s stop fighting about it; let’s stop trying to prove our points, and try to discover all the amazing things this world has to offer, may science prevail at helping us understand the truth, and put our world in the perspective that God intended us to see it.

  7. Pingback: A creationist tries his luck with the SD «·

  8. The fact that no life has ever been discovered anywhere other than Earth does not disprove that life on our planet exists only because life adapted to our environment, but it has to raise the question. If it doesn’t science is dishonest with itself. If life happened and exists on this planet because it adapted to the environment over time, why would it not do the same with other environments, such as the environment on Mars or Venus or? Anything that even suggests that only the Earth is suited to support life also must suggest that the elements that support life here exist because of Earth’s position. For example, the Earth is a specific distance from the sun and the moon a specific distance from the Earth. If the Earth were any closer to the sun, it would be too hot for life too exist as we know it now. If the moon were any closer to the Earth, it would cause massive tidal waves and be unsafe to live near the shoreline. If it were any farther away, the moon would not have enough pull on the oceans and life in the oceans (as we know it) would die off. Evolution argues that life adapted to this environment, evolving to support itself in the temperature we live in, etc. If this were true, why wouldn’t such a theory suggest that there should also be life on other planets, especially those near to us? Why wouldn’t life adapt there as well? What makes our environment less harsh than another? It is not less harsh than Neptune, just different. If life evolved to survive in frozen nitrogen rather than 70 degree gaseous oxygen, Earth would be the harsh environment and Pluto might be more sufficient, correct? The FACT that the Earth is where it is and there is life on it, and the FACT that the moon is in the exact location it needs to be to keep the oceans clean on the Earth, and the FACT that the 23 1/2 degree tilt of the earth in relationship to the revolution of the Earth around the sun creates the perfection of the seasons and climates for the northern and southern hemispheres on the Earth SHOULD suffice a scientific theory that there is an intelligence to why Earth supports life and nothing else does. That the Earth supports life while no other celestial body does is scientific theory ever as much as evolution and gravity are, which should therefore also at least SUGGEST that there is intelligent design to life on Earth. To believe that it all just happened this way by accident is not only scientifically ridiculous but any scientist with a working brain would have to lie to himself to ignore the facts that our system is the only one that has the ability to support life. In my own reasoning, there is NO EXPLANATION as to why the Earth alone would support life if evolution were true. BTW, I’m NOT trying to prove a religion based on disproving evolution, but I personally hold the “theory” of evolution to the same standards as you might a religion. I find that it fails miserably in MANY ways and no one has ever been able to convince me otherwise. I find that people just don’t think deeply enough about what they hear before they accept it.

    • 1) Life arose on Earth thanks to the conditions of the planet. Why didn’t life arise in any of the other planets? Because the conditions wouldn’t allow it. You must first understand what is needed to create life as we know it.

      2) There is no reason to believe that life on earth was the product of an intelligence. The origin of life on earth can be explained through natural means alone. It’s just chemistry. It was in a sense an accident as much as raining is an accident. It is a natural process bound to happen when certain conditions are met.

      3) The theory of Evolution (which is a fact, scientific theories all are) makes no attempt to explain how life began nor why life appears exclusive to Earth. That is abiogenesis and it’s a complete scientific realm on its own. All evolution explains is the ‘diversity’ of life once it already happened. First life occurs THEN evolution can start doing its thing.

      4) The ‘appearance’ of design does not warrant a designer. Besides, if you are going to claim an intelligence is behind life, it begs the question; how would life look like if there was NO intelligence behind it?

      5) Religion can’t hold up to the same standards as evolution. To begin with, religious belief can not be falsified. Evolution can. Evolution presents evidence you can test and which help make predictions about the world that surrounds us. Religion does not. Evolution has been proven true time and again. Religion has always been and will always be based on blind faith.

      • 1)Once again based on assumption. Assuming that the only condition for life is the conditions found on earth.

        2)IF it is just chemistry, where did the information come from. IE where did the single cell amoeba get the DNA information to produce an eye, etc.

        3)The theory of evolution is not fact, it cannot be proven. You cant test theories presented in evolution. First problem, dating mechanisms are flawed. Second. There is no control. Third there is no direct observance.

        5 Evolution has been proven false time and time again. Don’t give one side of the story

        • Obviously, someone was not paying attention…
          2) Just because the science does not know or cannot explain certain phenomena, does not automatically imply God must exist. Fallacy #7 (Confusing unexplained with unexplainable).

          • Nobody said that means God exists. We’re simply talking about the flaws of evolution. You’re dodging the meat of the criticism.

  9. Hi, thanks for this! It does seem as if #17. can be posted under #2 in all cases. My old logic book from Irving Copi used the apochraphal tale of copernicus debating with the theologians about the imperfections in the heavenly bodies as able to be seen through his telescope. The theologians answered it was false, the holes were actually filled with a clear crystalline substance. Copernicus respondes that, in fact, there were still imperfections in the form of great mountains of that substance!

    Hope this helps.

    Thanks again!

  10. Pingback: Top 20 Logical Fallacies « Shining light on ignorance·

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