Logic in Everyday Life
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
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…
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.
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
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.
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?
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.
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
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…