Logical Fallacies
Published on Nov 19, 2015
Created with the material provided by Dr. Joe Miller at University of Virginia.
MORE DECKS TO EXPLORE
PRESENTATION OUTLINE
If you weigh the same as a duck,then, Logically,
you're made of wood and must be a witch.
Photo by kevin dooley
Argument:
Aconclusion together with the premises that support it.
Premise:
A REASON OFFERED AS SUPPORT FOR ANOTHER CLAIM.
Conclusion:
A claim that is supported by a premise.
Valid:
An argument whose premises genuinely support its conclusion.
Unsound:
An argument that relies upon faulty reasoning.
Fallacy:
An argument that relies upon faulty reasoning.
Booby-Trap:
Is not a fallacy but might lead an reader to commit a fallacy.
Examples
Basketball
- Whichever basketball team scores the most points will win the game
- The team that scores the most points wins the game.
- Ferris scored more points than Van.
- Therefore Ferris won the game.
Photo by BozDoz
Basketball
- What are the premises?
- What is the conclusion?
- Is the argument valid?
- Why or why not?
The first two sentences are premises and the third is the conclusion. The argument is valid, for the two premises provide genuine support for the conclusion.
Photo by HckySo
Presidential Elections
- The candidate that receives most of the popular vote will win.
- Al Gore received more votes than George Bush.
- Therefore, Al Gore was elected President of the United States.
Photo by DonkeyHotey
Presidential Elections
- What are the premises?
- What is the conclusion?
- Is the argument valid?
- Why or why not?
The first two sentences are premises, and the third sentence is the argument's conclusion. The first premise is false. Getting the most votes is not the way one gets elected president. This is an unsound argument.
Photo by DonkeyHotey
Why do arguments fail?
False Premise
- If Burger King sells Big Macs, then McDonald's will go out of business.
- If Burger King sells Big Macs, then McDonald's will go out of business.
- If Burger King sells Big Macs, then McDonald's will go out of business.
- Burger King does sell Big Macs.
- Burger King does sell Big Macs.
- There
- Therefore, McDonald's will go out of business.
Photo by monkeyc.net
Conclusions Do Not Follow the Premises
- Baptist
- Baptists are often politically conservative.
- Republicans are often politically conservative.
- Therefore, Baptist are often republicans.
Photo by Joel Abroad
Conclusions do not follow the premises
- John Elway is a great quarterback.
- Troy Aikman is a great quarterback.
- Therefore, Troy Aikman is really John Elway.
Photo by Jim Nix / Nomadic Pursuits
Wrapping Up
- Picking out fallacies is more art than science.
- Picking out fallacies is more art than science.
- Some arguments are bad but not fallacies.
- Some arguments are bad but not fallacies
- Some are so bad they have more than one fallacies.
Ultimately, It is more important to...
understand why an argument is bad than to be able to name it.
