Logic in Everyday Life

1. Logic in Everyday Life

2. Zeno’s Paradoxes • Stuck in School Forever is an example of deductive reasoning: • To reach the door involves passing an infinite number of halfway points • Passing an infinite number of halfway points will take an infinite amount of time. • Therefore you will never reach the door

3. Deductive vs. Inductive • Deductive arguments move from the general to the particular, vs. inductive arguments that move from the particular to the general: • For example…

4. All humans are mortal • I am a human • Therefore, I am mortal • Is a deductive argument. • A deductive argument is also known as a syllogism. • The basic syllogism contains two premises and a conclusion. • In the above argument, the first two statements are premises, the third is the conclusion.

5. An Inductive argument moves from the particulars to the general. For example: • Thales is mortal • Socrates is mortal • Plato is mortal • Aristotle is mortal • Einstein is mortal • Therefore all humans are mortal

6. Validity vs. Truth • Logic is based on Aristotle’s Three Laws of Thought: • Law of non-contradiction • 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 same time. • Law of the excluded middle • 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 does not exist. • Law of identity • Says that something is what it is. For example, Tom is Tom, and Ricky is Ricky. To say “Tom is Ricky” is untrue. • In order for an argument to be valid, it must conform to these basic principles.

7. The validity of an argument is based on correct reasoning. When assessing an argument you must distinguish between validity and truth. For example: • All humans are immortal • I am a human • Therefore, I am immortal • Is this a valid or invalid argument?

8. Even though the major premise (All humans are immortal) is untrue, this argument is still valid because the conclusion follows logically from the premises. • Deductive arguments are always either valid or invalid… • The same cannot be applied to inductive arguments, which are usually based on probability and are known as either strong (reliable) or weak.

9. Logic and Everyday Life • Using logic and good reasoning skills matters in everyday life. Logical reasoning helps us to: • Accomplish tasks • Evaluate what people say • Assess what you see and hear in the media • Justify decisions • Justify actions • Help distinguish facts from opinion

10. Judge Judy… • Students will get into groups of four. • We will watch three excerpts from the TV show Judge Judy. • Using the Analyzing an Argument handout each student is to take notes regarding the logic and effectiveness of the arguments presented. • At the end of the viewing students will get into their group to discuss and compare notes. • 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. • Go to the Judge Judy Show…