Logical fallacies

• Problems with premises• Premise is false• Premise is an unwarranted assumption• Hidden premise

Ad hominem

• Attacking the person• UFO sighters are crazy• Members of the government must be lying because they are

corrupt• Name calling in itself is not a logical fallacy• “poisoning the well”• His argument is just like Hitler’s position

Appeal to authority

• Claim held by individual is true because that person speaks from authority• Airline pilots• Judges• Professors• Popular belief• Antiquity

• Similar to ‘appeal to nature’ – because something is natural it is justified

Begging the question

• Assuming that the conclusion is true in one of the premises

• Example:• “How long has it been since you stopped beating your

wife?”• Similar to tautology• Circular reasoning – conclusion is also the premise

Red herring

• Adding a ‘premise’ in order to distract the opponent from the real argument

False cause

• Assuming that two events are linked by cause when they may be just coincidental• Correlation in a controlled experiment, though, may suggest

causation• Similar to post-hoc ergo propter hoc• “After this, therefore because of this”

False analogy

• Assuming that two events / ideas are similar when they have some important difference

• Similar to composition / division• What’s true about one part of something has to be true for

all

Non-sequitur

• “doesn’t follow”• No logical connection exists

Slippery slope

• Assuming that, if you accept one premise, you also have to accept more extreme cases

• “if A happens, then Z will happen too. Therefore, A shouldn’t happen”

Black-or-white

• “either-or”, false dichotomy• Falsely assumes that there are only two alternatives

Special pleading

• Adding new premises to respond to critics and strengthen the argument

• Changing the rules of the game as you go • Similar to “moving goalpost”• Changing the criteria for a good argument if the opponent

comes up with evidence• Called ad-hoc reasoning

Straw Man

• Making the opponent’s argument into a position that is easier to attack

Hasty generalization

• Basing a conclusion on insufficient or biased evidence

Tu quoque

• “you too”• Responding to criticism by attacking the critic• Similar to ad hominem

Appeal to emotion

• Ad populum • Appeal to positive emotions (e.g. patriotism)• Appeal to negative emotions (e.g. fear)• May include slippery slope, irrelevant thesis, etc.

• http://atheistuniverse.net/photo/thou-shalt-not-commit-logical-fallacies

• http://www.theskepticsguide.org/resources/logicalfallacies.aspx

• http://owl.english.purdue.edu/owl/resource/659/03/