Fallacies are defects in an argumentwhich cause an argument to be invalid,unsound or weak.

An appeal to ignorance occurs when one person uses another person’s lack of knowledge on a particular subject as evidence that their own argument is correct.

For example: “You can’t prove that there aren’tMartians living in caves under the surface of Mars,so it is reasonable for me to believe there are.”

This type of fallacy is also referred to as Argumentum ad Verecundia (argument from modesty). In this case, rather than focusing on the merits of an argument, the arguer will try to attach their argument to a person of authority in an attempt to give credence to their argument.

For example: “Well, Isaac Newton believed in Alchemy, do you think you know more than Isaac Newton?”

This type of appeal is when someone claims that an idea or belief is true simply because it is what most people believe.

For example: “Lots of people bought this album, so it must be good.”

Sometimes called "guilt by association," this occurs when someone links a specific idea or practice with something or someone negative in order to infer guilt on another person.

For example: “Hitler was a vegetarian, therefore, I don’t trust vegetarians.”

Also known as Argumentum ad Hominem (argument against the man), this is quite a common occurrence in debates and refers to a person who substitutes a rebuttal with a personal insult.

For example: “Don’t listen to Eddie’s arguments on education, he’s an idiot.”

Also referred to as Circulus in Probando, this fallacy is when an argument takes its proof from a factor within the argument itself, rather than from an external one.

For example: “I believe that Frosted Flakes are great because it says so on the Frosted Flakes packaging.”

Otherwise known as Cum Hoc Ergo Propter Hoc, this is a fallacy in which the person making the argument connects two events which happen sequentially and assumes that one caused the other.

For example: “I saw a magpie and ten minutes later, I crashed my car, therefore, magpies are bad luck.”

Sometimes referred to as Bifurcation, this type of fallacy occurs when someone presents their argument in such a way that there are only two possible options.

For example: “If you don’t vote for this candidate, you must be a Communist.”

A fallacy where in someone asserts a conclusion that does not follow from the propositions.

For example: “All Dubliners are from Ireland. Ronan is not a Dubliner, therefore, he is not Irish.”

Assuming that a very small action will inevitably lead to extreme and often ludicrous outcomes.

For example: “If we allow gay people to get married, what’s next? Allowing people to marry their dogs?”

bases an inference on too small a sample, or on an unrepresentative sample. Often, a single example or instance is used as the basis for a broader generalization.

example: All of those movie stars are really rude. I asked Kevin Costner for his autograph in a restaurant in Westwood the other evening, and he told me to get lost.

A fallacy very similar to slippery slope, which involves taking an argumentative claim or assertion to its extreme, even though the arguer does not advocate the extreme interpretation. The difference between the two fallacies is that appealing to extremes does not necessarily involve a sequence of causal connections.example: Husband to ex-wife: Well, if you want to be completely fair about dividing everything up, you should get one of my testicles and I should get one of your breasts!

This fallacy consists of offering a poorly supported claim

about what might have happened in the past or future if

circumstances or conditions were other than they

actually were or are. The fallacy also involves treating hypothetical situations as if they were fact.

EXAMPLE: If Hitler had not invaded Russia and opened up two military fronts, the Nazis would surely have won the war.