I have been asked to write a summary of logical fallacies (I have used multiple sites and sources - if you want to find more information type logical fallacies into your search engine).
What is an argument?
An argument is a connected series of statements to establish a definite proposition. A proposition is a statement which meaning is either true or false.
If we’re interested in establishing A, and B is offered as evidence, the statement “A because B” is an argument. If we’re trying to establish the truth of B, then “A because B” is not an argument, it’s an explanation.
The most precise and the most persuasive are deductive arguments which provide conclusive proof of their conclusion. (they can be either valid or invalid). Deductive arguments have three stages: premises, inference, and conclusion.
Premises are the core assumptions on which the argument is built on (Since… Because…). They are the reasons for accepting the argument. Premises are only premises in the context of a particular argument. One should always state the premises of the argument explicitly and it is a good idea to get your opponent to agree with the premises of your argument before proceeding any further.
Once the premises have been agreed, the argument proceeds via a step-by-step process called inference. In inference (…therefore… or…implies…), you start with one or more propositions which have been accepted and then use those propositions to arrive at a new proposition. If the inference is valid, that proposition should also be accepted. You can use this new proposition for inference later on.
Hopefully you will arrive at a proposition which is the conclusion of the argument - the result you are trying to prove. The conclusion is the result of the final step of inference. It’s only a conclusion in the context of a particular argument but it could be a premise or assumption in another argument.
Spotting an argument is harder than spotting premises or a conclusion. Lots of people shower their writing with assertions, without ever producing anything you might reasonably call an argument.
There are a number of common pitfalls to avoid when constructing a deductive argument; they’re known as fallacies. A fallacy is a technical flaw which makes an argument unsound or invalid. (there are too many to list them all here - I will just pick few which I think are the most relevant here).
Argumentum ad hominem (argument directed at the man)
Abusive form:
example: You claim that atheists can be moral – yet I happen to know that you abandoned your wife and children.
(This is a fallacy because the truth of an assertion doesn’t depend on the virtues of the person asserting it.)
or
to reject a proposition based on the fact that it was also asserted by some other easily criticized person.
example: This sounds like something Hitler would say.
an attack on the bias of a person:
example: Sure you would say that tobacco companies have a right to exist - you are as smoker.
guilt by association:
example: You are pro-choice but lets not forget that communists are also pro-choice therefore you are a communist.
Argumentum ad ignorantiam (argument from ignorance - something is true because it has not been proven wrong)
example: Of course the Bible is true. Nobody can prove otherwise.
Argumentum ad numerum
example: All I’m saying is that thousands of people believe in pyramid power, so there must be something to it
Appeal to Authority
example: Newton was a genius and he believed in God.
Circulus in demonstrando
circular argument: the premise is the same as the conclusion
Begging the question
(the premises are at least as questionable as the conclusion reached - the premises of the argument implicitly assume the result which the argument purports to prove)
example: If such actions were not illegal, then they would not be prohibited by the law.
Red herring
introduction of irrelevant material to the issue being discussed, so that everyone’s attention is diverted away from the points made, towards a different conclusion.
example: You may claim that the death penalty is an ineffective deterrent against crime – but what about the victims of crime? How do you think surviving family members feel when they see the man who murdered their son kept in prison at their expense?
The slippery slope argument
example: If we legalize marijuana then more people would start to take crack and heroin, and we’d have to legalize those too. Before long we’d have a nation full of drug-addicts on welfare.
Straw man
The straw man fallacy is when you misrepresent someone else’s position so that it can be attacked more easily, knock down that misrepresented position, then conclude that the original position has been demolished. It’s a fallacy because it fails to deal with the actual arguments that have been made.
example: To be an atheist, you have to believe with absolute certainty that there is no God. In order to convince yourself with absolute certainty, you must examine all the Universe and all the places where God could possibly be. Since you obviously haven’t, your position is indefensible.
Non sequitur
an argument where the conclusion is drawn from premises which aren’t logically connected with it.
example: Since Egyptians did so much excavation to construct the pyramids, they were well versed in paleontology
Equivocation
when a key word is used with two or more different meanings in the same argument
example: What could be more affordable than free software? But to make sure that it remains free, that users can do what they like with it, we must place a license on it to make sure that will always be freely redistributable.
Sweeping generalization
a general rule is applied to a particular situation, but the features of that particular situation mean the rule is inapplicable.
example: Most women like flowers. You are a woman, so you must like flowers.