Download Philosophy 103 Linguistics 103 Introductory Logic

Philosophy 103
Linguistics 103
Yet, still, Even More
Introductory Logic:
Critical Thinking
Dr. Robert Barnard
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Informal Fallacies:
Fallacies of Relevance
Fallacies of Weak Induction
Fallicies of Meaning and Ambiguity
Laws of Thought?
Plan for Today
Try to wrap up Laws
of Thought
Start: Meaning and Definition
The “Laws of Thought”
1) Identity
2) Non-Contradiction
3) Excluded Middle
Are They all both General and
Necessary?
The Law of Identity
“A true statement is true.”
“All A is A.”
“Everything is what it is, and not
something else.”
“Everything is self-identical.”
The Law of Non-Contradiction
“ Nothing A is not A” (a form of ‘identity’?)
“No statement is both true and false at the same
time.”
“Nothing is both F and not-F at the same time.”
“Opposite qualities are incompatible.”
“Everything F is not not-F.”
The Law of Excluded Middle
“Every statement must be either true or false.”
“If something is F then it is not not-F.”
“Either F or not-F.”
The Laws of Thought…
… Are ways of thinking about LOGICAL
CONSISTENCY.
We do not always recognize what logic requires,
but we are fairly good at recognizing what is not
logically consistent:
- The Square Circle
- The Colorless red box
- The empty jar full of pennies.
Logic and Psychology
• Where do the laws of thought come from?
• Are they generalizations upon experiences?
• Could we arrive at their general correctness
without having a variety of experiences?
A problem for the Psychological
Account…
Suppose I accept a logical principle or law (e.g.
transitivity) [ X is prior to Y, Y is prior to Z, Therefore X
is prior to Z].
Suppose you also accept transitivity.
If you and I acquire transitivity based upon our
respective experiences, does this guarentee that MY
law of transitivity is the same as YOUR law of
transitivity?
What about “Addition”?
The laws of thought …
…are not best thought of as scientific laws
describing thought.
Instead they are better understood as
regulations governing rational thought.
New Topic:
Meaning and Definition
Meaning and Definition
The Logical Characteristics of a situation are not
determined by language.
How we understand a claim IS determined by
language.
Precise Language is required for Precise Thought
Meaning
There are several commonly recognized kinds of
linguistic meaning (kinds of significance)
• Cognitive [Conveys Information, Descriptive,
Fact Stating, could be true or false]
• Emotive [ Conveys Feeling, might not be fact
stating or true/false –Rhetorically useful]
• Normative [Evaluative]
Fact vs. Value
Descriptive claims attempt to give an account of how
the world is. This is Factual Meaning.
Normative claims attempt to give an account of how
the world ought to be, or grade the world relative to
a scale. This is Normative Meaning.
Issue: Are there Normative Facts?
Ambiguity
When a word, name, or term can be given more
than one meaning in a context, then we say
that the term is ambiguous in that context.
“I am going to the bank.”
“Are you sore?”
Intension and Extension in
Meaning
Cognitive Meaning (informational content) is
usually analyzed in terms of what we call
Extension and Intension .
• Extension tells us what a word or idea or concept
picks out.
• Intension tells us what the nature or essence of
the concept or idea is. The intension determines
the extension
Extension
The EXTENSION of a term (or idea or concept)
simply is the set of all objects or cases that are
picked out by the term.
• The extension of ‘cat’ is all cats.
• The extension of ‘blue’ is all blue objects.
• The extension of ‘American States’ is the 50
States.
Intension
The INTENSION (with an S) of a term (or idea or
concept) is the definition of the term. It is the
rule according to which something either is or
is not part of the extension of the term.
The INTENSION of ‘human being’ is something
like: “bipedal mammal of the genus homo,
species sapiens, capable of reason and
humor.”
Alternate Vocabulary
The Intension/Extension distinction is
sometimes called:
• Sense/Reference
• Connotation/Denotation
Names and Descriptions
Both Proper Names and Descriptive Phrases can
precisely pick out a specific individual or group.
• Sometimes names are names for descriptions,
not objects.
• But one individual or group may have more than
one name or description.
• Also not every description will be definite
enough to pick out a specific target.
Proper Names / Descriptions
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Al Gore (name)
Alberto Gonzales (name)
The Attorney General (description)
The former vice-President (description)
The Sultan of Bhutan (description)
The author of The Firm (description)
The Chancellor of the University of Mississippi
(description)
• A lawyer from New York (imprecise description)
Different Terms, Same Object
The Morning Star vs. The Evening Star (Venus)
Superman vs. Clark Kent (Kal El the Kryptonian)
The victor at Austerlitz vs. the loser at Waterloo
(Napoleon)
Mark Twain vs. Samuel Clemens
(that guy who wrote Huck Finn)
Some Interesting Cases
• Conventional Connotation
– When a term has a conventional meaning that
governs its usual interpretation
• “White House” (Is there only one?)
• “Western” “Rational” “All-American”
(suppressed content/value judgements?)
• Empty Extension
– When a term has a well understood intension but
there is no object in the extension
• unicorn
• Santa Claus
• The present King of France
What does a description REALLY say?
A description is a useful device for recognizing the
difference between what language expresses
(surface meaning) and what is actually said
(logical analysis).
“The present king of France is bald.” (Russell 1905)
There is a person. The person in question is the
King of France. If the person in question is the
King of France, then he is also bald.
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