Logic, inductive and deductive reasoning.

1. SKILLS IN PHILOSOPHY – THE
IMPORTANCE OF LOGIC AND
GOOD REASONING

2. THE CHEWBACCA DEFENCE:
A SOUTH PARK LESSON IN LOGIC
Logic is the study of
the principles of
correct reasoning
associated with the
formation and
analysis of
arguments.

3. LOGIC IN ACTION
In groups use your powers or reasoning
and logic to solve the answer to the
following puzzles.

4. LOGIC
In Star Trek when Spock is referred to as
being ‘logical’ it is usually taken to
mean that he is without emotion.
Sherlock Holmes is considered similarly
‘cold’. Why is this? And what is being
‘logical’ anyway?

5. Introduction – The master of
deduction
 In one mystery concerning the
theft of an expensive racehorse, a
police officer asks Sherlock
Holmes if any aspect of the crime
strikes him as significant. ‘Yes’, he
says ‘the curious incident of the
dog in the night time’. The dog
did nothing in the night time’
says the hapless police officer.
‘That was the curious incident’,
replies Holmes.
 How has Holmes deduced the
solution to the crime?

6. Solution  The solution to the crime hinges
on the fact that the watchdog
guarding the horse did not bark
in the night, and from that
Holmes deduces that the thief
must have been known to the
dog. We can lay out Holmes
reasoning formally as follows:
 Watchdogs bark at
strangers.
 The watchdog did not bark
at the thief.
 Therefore the thief was not
a stranger.

7. Argument
We argue in different ways: we quarrel, debate
or persuade. In a philosophical sense argument is
used to persuade others of your point of view.
Although quarrels may not have rules,
persuasion arguments do.
There are 2 categories of argument: Deductive
and Inductive.
A deductive argument provides conclusive
support for its conclusion as long as it is valid, an
inductive argument provides probable support
for its conclusion providing it supplies strong
evidence.

8. 1. Deductive argument is a
method of ascertaining
validity. A properly
constructed deductive
argument is valid so if all its
premises are true then its
conclusion must be true.

9. Aristotle (384-322BC) is credited with inventing deductive
arguments as a means to drawing conclusions. By looking at
his own example we can see the form deductive arguments
take:
If the question were asked ‘Is Socrates mortal?’
then the following deductive argument could be
applied.
All men are mortal (1st premise)
Socrates is a man (2nd premise)
Socrates is mortal (conclusion)
The conclusion follows from the premise. A valid deductive
argument will always lead to a valid conclusion but the truth
of the conclusion relies on the truth of the premises.

10. Cartman gives us another example.
•If the boys combine their lost teeth,
then they’ll get money from the
Tooth Fairy (premise 1)
•If they get money from the Tooth
Fairy, then they can buy a PS3 (premise 2)
-------------------------------------------
•Hence, if the boys combine their lost teeth
then they can buy a PS3 (conclusion)

11. 2. Inductive argument is a
method of ascertaining the
degree of certainty the premises
confer on the conclusion. A
properly constructed inductive
argument has strength in that if
all the premises are true then the
conclusion is probably true.

12. How sure are you that some day you will die?
What evidence do you have for your belief?
With reference to the above example, my belief
that all human beings are mortal is based on the
observation that in history, every human being I
know of has eventually died, and I have never
heard of a human being who didn’t die.
Therefore, I can say with confidence that ‘all
observed human beings have died’.
Our inductive reasoning can therefore lead us to
the conclusion that ‘all human beings are
mortal’.

13. South Park offers another example:
•Because in the past when we
mentioned towel related things,
Towelie has always showed up.
(premise 1)
•And because we will mention
something towel related now.
(premise 2)
-------------------------------------------------
We can conclude that Towelie will show
up. (conclusion)

14. Or, according to Cartman
•If you do drugs, then you are a
hippie (premise 1)
•If you are a hippie, then you
suck (premise 2)
•If you suck, then that’s bad
(premise 3)
So, if you do drugs, then thats
bad (conclusion)

15. In groups
 Come up with 2 examples of both an
inductive and deductive argument

16. Final Thoughts
As students of philosophy you will need to debate and discuss
effectively using arguments based on evidence and sound rational
thinking. Using well established induced or deduced logic in order
to arrive at your truth claims will give far greater weight and
importance to your conclusions.
On an even more serious note it is through fallacious reasoning or
faulty reasoning that many people seem to make poor decisions.
In South Park the case is put forward in the episode called Chef Aid
where a prominent lawyer successfully applies the Chewbacca
defence to prove a point to the jury and acquit the record company
of being found guilty of copyright violations of Chefs original song.

17. This South Park portrayal of absurd reasoning is
funny in the cartoon. However its not so funny when
we see faulty reasoning at work in the real world.
Consider the following conclusions drawn.
All Jews are vermin
Vermin needs to be destroyed
All Jews need to be destroyed
OR
All terrorists are evil
All terrorists are Muslim
All Muslims are evil

18. OR
All Americans are immoral
Immorality is punishable by death
I will sacrifice my life to bring
death to Americans.
Logic is the study of the principles of correct reasoning
associated with the formation and analysis of arguments.
The way in which we reason affects the beliefs we have,
which ultimately affects the way in which we behave and live
our lives. Therefore, it is vitally important to reason correctly.