25 logical fallacies

Logical fallacies are instances where our reasoning goes wrong and I believe that nobody is immune. They’re important to recognise as they can enable you to spot mistakes in an argument.

Here are twenty-five of the most common logical fallacies:

1. Ad hominem
The tactic of responding to a statement by verbally attacking the person making it and not addressing the statement. Often met at paranormal conferences from members of the audience upset by skeptical lecturers. Great as a rabble-rouser!
Example 1: “You’re telling me that homeopathy is rubbish but you would say that as you used to work for a pharmaceutical company.”
Example 2: “Can you believe the word of a man who hasn’t taken the time to shave?”

2. Argument from authority
Support of a statement based upon the qualifications, experience, supposed reliability and authority of the claimant or those who support them.
Example: “I’ve worked as a meteorologist for twenty-five years so I can tell you that this crop circle could only be made by a whirlwind.”

3. Argument from final consequences
Popularised by a host of religious believers, this fallacy confuses the order of cause and effect. It suggests that the overall cause of an event is its own widest reaching effect.
Example: “Our planet supports life. Therefore it must have been created by some sort of god.”

4. Argument from ignorance
Claiming a statement is true on the basis that it has not been shown as false. (Swap the ‘true’ and ‘false’ around in the previous sentence and it still works just as well, see example two below.) A cornerstone in the defences of paranormal and religious believers.
Example 1: “I’ll go on believing in ghosts as nobody has proven they don’t exist!”
Example 2: “There is no way any human could ever have psychic powers; they’ve never been shown to be real.”

5. Argument from personal incredulity
Little more than arrogance: assuming a statement cannot be true because you don’t understand it.
Example: “Keep your science, it doesn’t make any sense to me. I know that ghosts are real.”

6. Argumentum ad hitlerum
A means of discrediting a statement through association with Adolf Hitler, his supporters or policies.
Example: “Hitler was an atheist. Atheism is wrong.”

7. Circular reasoning
Trying to support a statement by merely repeating the same statement in different words. Frequently used by the religious to prove their belief in a deity.
Example 1: “God is real because it says in the Bible that he exists.”

8. Composition fallacy
Applying a statement that is true of a constituent part of a whole to the total. Repeatedly used by paranormalists who extend the quantum physics of the micro world to the macro world without any supporting evidence.
Example: “You can’t see the cells in my body, so you can’t see me.”

9. Confusion of unexplained with unexplainable
The fallacy of assuming that because something is now unexplained it will remain unexplainable by science.
Example: “Science cannot explain those gaps in the fossil record. This means, without a shadow of a doubt, that the argument for evolution is false.”

10. Cum hoc ergo propter hoc
When two events occur at the same time it may be tempting to fall into the trap of assuming, without further examination, one has caused the other.
Example: “Statistics show that the riots occurred at the same time as a rise in the popularity of rap music. The press claim that rap music sparked the rioting.”

11. Emotional appeal
What better way to show the supposed truth of a statement by avoiding or combining supporting evidence with tugs on the heart-strings? Frequently used in ‘believers versus skeptics’ type arguments.
Example 1 (fear): “If you believe this person’s view that crop circles are created by humans then you’ll be left with nothing for all those long years of research.”
Example 2 (pity): “How can you not accept the word of a man who has been through such torture and ridicule for his beliefs?”
Example 3 (unpopularity): “You may be tempted to agree with her but if you do so I can guarantee that you will be in the minority.”

12. Every schoolboy knows
Pre-emptive praising of one’s own statement by implying the point being made is extremely obvious; if you disagree then your level of understanding is below that of a schoolboy.
Example: “Every schoolboy knows that William the Conqueror died in 1065.”

13. Fallacist’s fallacy
A statement may be supported by fallacious arguments – but is that statement necessarily wrong? If not, and you’ve dismissed the statement because of the fallacies, you’ve demonstrated the fallacist’s fallacy. Learn from it.
Example: “You’re telling me I should just accept the existence of gravity because you’ve got a doctorate? No chance, all you’re doing is arguing from authority.”

13 & a bit (I can’t count!). False dilemma
The ploy of reducing the possible solutions to an issue down to two. Very often these choices may be framed as a ‘yes or no’ or ‘black and white’ scenarios, thereby oversimplifying things and neglecting alternative possibilties.
Example: “You’re either with me on this or you’re against me.”

14. Genetic fallacy
Failing to assess a statement on its merit and instead judging it on its origins.
Example: “Of course I don’t like anyone from Scotland. My parents told me they’re all psychotic and so they must be.”

15. God of the gaps
Explaining away gaps in human knowledge by attributing them to a supernatural cause.
Example: “We don’t know how life appeared on this planet; this must be evidence for Zeus’s existence”

16. Hasty conclusion
As the name suggests this is the error of jumping to a conclusion without examining all the available evidence. A favourite of armchair jury members.
Example: “He was seen in the area at the time of the robbery so he must have been responsible.”

17. Moving the goalposts
Dismissing previously agreed, acceptable evidence in support of a claim and demanding it be of a higher quality.
Example: “Okay, we’ve seen a copy of Obama’s birth certificate, now let’s see the original in its long form.”

18. Naturalistic fallacy
Establishing the worthiness of something due to it being considered ethically ‘good’. In recent times the fallacy has become increasingly used as an appeal to nature. Loved by alternative medicine practitioners and snake oil salesmen alike.
Example: “Eating these mushrooms is perfectly safe; they’re 100% natural.”

19. Poisoning the well
An attempt to discredit an opponent’s statement by pre-emptively linking them to another unfavourable position, organisation or individual.
Example: “Before I examine my opponent’s policies consider whether you can trust him as a close friend of my discredited predecessor.”

20. Post hoc ergo propter hoc
Literally “after this, therefore because of this”; assuming that two events are related because one occurs after the other.
Example: “After John went in the direction of the police station the officers raided my house. John must have tipped them off.”

21. Shifting the burden of proof
Closely related to the argument from ignorance. It’s the job of someone making a statement to demonstrate its validity with supporting evidence. They shift the burden of proof when they fail to do this and instead challenge doubters to show evidence that disproves the statement. Another form of lame defence often trotted out by firm believers in the supernatural.
Example: “Skeptics keep telling me that I’m wasting my time running my yeti website. I’ll keep believing in the yeti until they prove it isn’t real.”

22. Slippery Slope
Requesting the banning or curtailment of something on the unsubstantiated, unprecedented grounds that it will lead to negative consequences. The favourite fallacy of Disgusted of Tunbridge Wells and countless other Daily Mail readers.
Example: “Harry Potter books must be banned. Before we know it our playgrounds will be full of children practising magic and forgetting the word of the Bible.”

23. Special pleading
The flawed step of recognising a rule yet making unjustified exemptions.
Example: “I was given the same dowsing experiment as everyone else. We all failed but I did so only because there was a skeptic in the room.”

24. Strawman
Refuting a statement by disregarding at least some of its key elements. By attacking a distorted version of a statement the original point remains unaddressed.
Example: “I don’t see how Darwinists can claim we’re descended from monkeys!”

25. Tu quoque
Meaning ‘you too’, this fallacy is essentially an appeal to hypocrisy. Pointing out that an opponent is guilty of the very thing they are criticising is not grounds in itself for dismissing a statement. Remember, two wrongs do not equate to a right.
Example: “You’re telling me that I shouldn’t be taking drugs but I saw you doing it this morning.