REASONDaniella Silva, Jessica de Medeiros, Sebastian Salomón,

Sebastian Ríos, Vincenzo Calvi, Antonella Busato, Heechae Chon

Sherlock Holmes: ‘crime is common, logic is rare’ 

Using reason to go beyond the immediate evidence of our senses

Saving time by inferring from something you already know

Assumptions = premises Rationalism = reason as a source of knowledge

◦ Discovering truths about reality through reason alone (math/logic)

◦ Recognizing that senses can easily mislead us

INTRODUCTION

3 kinds of reasoning:◦ deductive reasoning◦ inductive reasoning◦ informal reasoning

Fallacies – invalid patterns of reasoning  

Reasoning that moves from the general to the particular Syllogisms

◦ Two premises and conclusion◦ Three terms, each occurring twice◦ Quantifiers

Defining Truth and Validity◦ Truth = property of statements◦ Validity = property of arguments (whether conclusions follow

logically from premises) Structure of Arguments

◦ As long as structure is valid, argument is valid◦ Analyzing structure helps avoid belief bias◦ Belief Bias = tendency to belief that an argument is valid just

because we agree with the conclusion

DEDUCTIVE REASONING

What about Truth?◦ Just because an argument is valid, does not mean

conclusion is true◦ In order for conclusion to be true: premises must be true

and argument must be valid◦ Example: ◦ Socrates is mortal, since all men are mortal.◦ It is evident that a tacitly understood claim is that Socrates

is a man. The fully expressed reasoning is thus: Since all men are mortal and Socrates is a man, Socrates is mortal.

◦ In this example, “all men are mortal” and “Socrates is a man” are the premises, while “Socrates is mortal” is the conclusion.

Enthymemes◦ Incomplete argument where one premise is not stated

because it is obvious

It is opposite to deductive reasoning It goes from the particular to the general It moves from the observed to the unobserved You reason inductively thousands of times a day Examples:  

◦ “Since my neighbor’s dog was friendly to me in the past, he will not bite me today”

◦ “Since apples nourished me in the past, I assume that they will nourish me in the future”

◦ “Since my chair supported my weight in the past, it will support me today”

INDUCTIVE REASONING

◦ We cannot always rely on it◦ Induction goes beyond immediate evidence of

our senses◦ Too much generalizations◦ You jump to conclusions without enough

evidence◦ This is called confirmation bias

How Reliable is it?

Informal reasoning is related to fallacies which are false ideas or beliefs, especially one that a lot of people believe is true.

There are several types of informal reasoning like ad ignorantiam, ad hominem, circular reasoning, special pleading, post hoc ergo propter hoc, equivocation, false analogy, false dilemma, and loaded question.

 

INFORMAL REASONING

Circular reasoning: Assuming the truth of what you are supposed to be proving. ◦ Example: ‘I know that Jesus was the son of god because

he said he was, and the son of god would not lie’

SPECIFIC EXAMPLES

Equivocation: using language ambiguously.◦ Example: ‘A feather is light.◦ What is light cannot be dark.◦ Therefore, a feather cannot be dark.’

Loaded question: A question that is biased because it contains built-in assumption. ◦ Example: ‘Do you always cheat in exams?’ Both yes/no

answers could imply something. Special pleading: using double standards to

excuse an individual or group. ◦Example: ‘I know there is a drought on and we

should save water, but I am putting my prize flowers in a competition next week and they need plenty of water.

Cannot rely on reason to give us knowledge

As a way of thinking, logical reasoning cannot be doubted.

The law of identity The law of non-contradiction The law of the excluded middle All proof must end somewhere

◦ Infinite regress: A sequence of reasoning that can never come to an end.

REASONING AND CERTAINTY

Law of identity

Law of non-contradiction

Law of the excluded middle

◦ Reason is a way of knowing that can give us certainty◦ Three types: inductive, deductive, informal ◦ This belief may bring serious doubt◦ Reason is a double-edged tool◦ We become trapped in the “prison of logic” and this

can stifle our creativity◦ Someone too rationale may come across as cold and

“annoying”◦ Sometimes empathy and understanding helps solve

an argument in a relationship rather than using logic and reason

◦ Reason needs to be balanced by emotion

CONCLUSION

http://www.youtube.com/watch?v=ZkajIoi77BU&feature=channel

http://www.youtube.com/watch?v=J2wj4Lk07RE&feature=channel

http://en.wikipedia.org/wiki/Premise

BIBLIOGRAPHY