Logic in Everyday LifeLogic in Everyday Life

Zeno’s ParadoxesZeno’s Paradoxes

Stuck in School Forever is an example of Stuck in School Forever is an example of deductive reasoning:deductive reasoning:

To reach the door involves passing an infinite number of halfway To reach the door involves passing an infinite number of halfway pointspoints

Passing an infinite number of halfway points will take an infinite Passing an infinite number of halfway points will take an infinite amount of time.amount of time.

Therefore you will never reach the doorTherefore you will never reach the door

Deductive vs. InductiveDeductive vs. Inductive

Deductive arguments move from the general to the Deductive arguments move from the general to the particular, vs. inductive arguments that move from the particular, vs. inductive arguments that move from the particular to the general:particular to the general:

For example…For example…

All humans are mortalAll humans are mortal

I am a humanI am a human

Therefore, I am mortalTherefore, I am mortal

Is a deductive argument.Is a deductive argument.

A deductive argument is also known as a syllogism.A deductive argument is also known as a syllogism.

The basic syllogism contains The basic syllogism contains two premisestwo premises and a and a conclusionconclusion..

In the above argument, the first two statements are premises, the third is the In the above argument, the first two statements are premises, the third is the conclusion.conclusion.

An Inductive argument moves from the An Inductive argument moves from the particulars to the general. For example:particulars to the general. For example:

Thales is mortalThales is mortal

Socrates is mortalSocrates is mortal

Plato is mortalPlato is mortal

Aristotle is mortalAristotle is mortal

Einstein is mortalEinstein is mortal

Therefore all humans are mortalTherefore all humans are mortal

Validity vs. TruthValidity vs. Truth

Logic is based on Aristotle’s Three Laws of Logic is based on Aristotle’s Three Laws of Thought:Thought:

Law of non-contradictionLaw of non-contradictionSomething cannot be said both to be and not to be at the same time and in the same respect. For Something cannot be said both to be and not to be at the same time and in the same respect. For example, if the statement “Tom Exists” is true, it cannot also be false. Tom cannot exist and not exist at the example, if the statement “Tom Exists” is true, it cannot also be false. Tom cannot exist and not exist at the same time.same time.

Law of the excluded middleLaw of the excluded middleSomething must either be or not be. For example, the statement “Ricky exists” must be Something must either be or not be. For example, the statement “Ricky exists” must be either true or false. There is no third or middle, possibility. Either Ricky exists or he either true or false. There is no third or middle, possibility. Either Ricky exists or he does not exist.does not exist.

Law of identityLaw of identitySays that something is what it is. For example, Tom is Tom, and Ricky is Ricky. To say Says that something is what it is. For example, Tom is Tom, and Ricky is Ricky. To say “Tom is Ricky” is untrue.“Tom is Ricky” is untrue.

In order for an argument to be valid, it must In order for an argument to be valid, it must conform to these basic principles.conform to these basic principles.

The validity of an argument is based on The validity of an argument is based on correct reasoning. When assessing an correct reasoning. When assessing an argument you must distinguish between argument you must distinguish between validity and truth. For example:validity and truth. For example:

All humans are immortalAll humans are immortal

I am a humanI am a human

Therefore, I am immortalTherefore, I am immortal

Is this a valid or invalid argument?Is this a valid or invalid argument?

Even though the major premise (All humans are Even though the major premise (All humans are immortal) is untrue, this argument is still valid because immortal) is untrue, this argument is still valid because the conclusion follows logically from the premises.the conclusion follows logically from the premises.

Deductive arguments are always either valid or invalid…Deductive arguments are always either valid or invalid…

The same cannot be applied to inductive arguments, The same cannot be applied to inductive arguments, which are usually based on probability and are known as which are usually based on probability and are known as either strong (reliable) or weak.either strong (reliable) or weak.

Logic and Everyday LifeLogic and Everyday Life

Using logic and good reasoning skills Using logic and good reasoning skills matters in everyday life. Logical reasoning matters in everyday life. Logical reasoning helps us to:helps us to:

Accomplish tasksAccomplish tasks

Evaluate what people sayEvaluate what people say

Assess what you see and hear in the mediaAssess what you see and hear in the media

Justify decisionsJustify decisions

Justify actionsJustify actions

Help distinguish facts from opinionHelp distinguish facts from opinion

Judge Judy…Judge Judy…

Students will get into groups of four.Students will get into groups of four.

We will watch three excerpts from the TV show Judge Judy.We will watch three excerpts from the TV show Judge Judy.

Using the Using the Analyzing an Argument handoutAnalyzing an Argument handout each student is to take notes each student is to take notes regarding the logic and effectiveness of the arguments presented.regarding the logic and effectiveness of the arguments presented.

At the end of the viewing students will get into their group to discuss and At the end of the viewing students will get into their group to discuss and compare notes.compare notes.

Each group will select an example of either a strong or a weak argument, Each group will select an example of either a strong or a weak argument, present it to the class, and explain the reasons for the assessment.present it to the class, and explain the reasons for the assessment.

Go to the Judge Judy Show…Go to the Judge Judy Show…