Transcript Philosophy of Science

Philosophy of Science
Psychology is the science of
behavior. Science is the study of
alternative explanations.
We need to understand the
concept of an explanation.
Explanation
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An explanation is an answer to the
question, “Why did/does that happen?”
An explanation is also called a “theory.”
It consists of statements from which one
can deduce the phenomena to be
explained.
It must satisfy several criteria.
Criteria for Explanation
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Deductive
Meaningful
Predictive
Causal
General
Before we can understand the
Criteria of Explanation, we
need to understand types of
statements.
Types of Statements
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Definitions= statements of equivalence in
language.
Logical Statements= a priori true or false,
based on logical analysis.
Empirical= statements whose truth is
tested a posteriori—i.e., by observations of
the “real world.”
Definition
A Definition is a statement of equivalence.
For example,
“A Bachelor is defined as a human male
who has never been married.”
A definition is neither true nor false.
However, it would be confusing to use
terms differently from those accepted by
convention (e.g., as in dictionary).
Operational Definition
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An Operational Definition is a definition
that specifies the operations of
measurement.
For example, operational definitions of
“male” might be based on external
genitalia, chromosomes, hormones,
internal organs, birth certificate, gender
identity, sexual orientation, clothes, etc.
Logical Statements
A logical statement is one whose truth is tested by
logical analysis. A logical statement is a priori
true or a priori false.
For example, “Some bachelors are married”
is a priori false. We do not need to conduct a
survey of bachelors to know that this statement
is false. All we need do is realize that if a
bachelor is never married then he cannot now
be married. It contradicts the definition.
Logical Statements
The statement, “All bachelors are human” is
a priori true, because the definition of
bachelor is that a person is human and male
and never married.
 The term for “and” is conjunction. The
symbol used in set theory is  . We can
write,
bachelor  {human  male  never married}
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Logical Statements
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“Some Bachelors are Married”
This is a priori false. We do not need to
do a survey; It contradicts the definition.
“Some Bachelors are female.”
This is a priori false, given the definition.
“Some Bachelors are human.”
A priori true, since all bachelors are
human.
Empirical Statements
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Empirical statements are statements
whose truth is tested a posteriori.
They are statements about the “real
world,” about observations we have made
or can make.
For example, “Some bachelors are taller
than 6 feet.”
This statement is a posteriori true,
because we have measured the heights of
human males who were never married
and found some who were this tall.
Deduction and Logic
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If the conclusion is true, does it follow
that the premises are true? NO!
Example:
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P1: All things made of cyanide are good to
eat.
P2: Bread is made of cyanide.
C: Therefore, Bread is good to eat.
Conclusion is true, but the premises are
false. So, a true conclusion does not
validate the premises.
Logic and Set Theory
Logic and set theory are closely related.
 “If A then B” can be rewritten as
 All As are B (i.e., A is a subset of B).
 A is a subset of B
 A implies B
 A  B
These ideas are really the same.
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Transitivity of Set Inclusion
If A is a subset of B (A  B)
 And if B is a subset of C (B  C)
 Then A is a subset of C (i.e., A  C).
 That is, if all As are B and all Bs are
C, then all As are C.
 Draw the Venn diagram with A inside
B, which is inside C.
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Transitivity of Implication
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AB
BC
Then A  C
In other words, if A then B
And if B then C
Then if A then C.
These are all the same underlying idea.
Meaning of Implication
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All As are B is true if and only if
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All not Bs are not A.
Put differently,
A  B  not B  not A.
Or:
A implies B if and only if
Not B implies not A.
Put another way:
If A then B  if not B then not A.
Example logic problem
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Conjecture: “All child abusers were abused
themselves as children.”
A Psychologist wants to test this
conjecture.
There are four lists of people, who are
known as abusers, victims, non-abusers,
and non-victims.
Types of Arguments
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Induction is an argument from past
occurrences to future events. It is based
on the “principle of induction” which holds
that past and future events are connected
by the same laws of nature.
Deduction is an argument based on
application of logic. A mathematical proof
is an example of deduction.
Generalizations
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A generalization is an empirical statement
that applies not only to instances at hand
but to future cases that have not yet come
to pass.
Generalizations include correlational and
causal statements.
Generalizations are made credible by
induction.
Induction
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Example of Induction:
If I drop a pencil, it will fall.
(this statement applies not only to one event,
but to an infinite number of possible future
events. There is an understood domain of
generality, such as we are near the earth and
there are no winds or magnetic fields, etc.)
We gather evidence by dropping pencils.
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Evidence for Induction
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The evidence consists of many repetitions
of the same observation.
A1B1
A2B2
A3B3
AnBn
At some point, n, we predict:
An+1Bn+1
Principle of Induction
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The principle of induction is not obvious to many
people. People who do not believe in induction
are called “existentialists.”
Some people argued that the principle is made
true by a God, who sees to it that natural laws
do not change.
Thus, the writers and philosophers who decided
that the Gods no longer exist, concluded that
induction no longer holds.
But they don’t jump off the 8th floor.
Improper Induction
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An old man decided that he would live
forever, based on the observation that every
night he went to bed alive, he woke up alive.
After 1000 nights, his belief that he would
live forever increased.
After 10,000 nights, his belief was even
greater.
What is wrong with the argument that he will
live forever?
Based on Induction over nights,
The old man thought he would live
forever. Day after day, he lived.
However, based on people, you think
that as he gets older, he is MORE
likely to die. Person after person, they all
died, so you don’t think he will live forever.
So the argument that he will not live
forever is also based on induction.
This example illustrates that the concept is
not a simple one.
Deduction
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Deduction is a logical enterprise, and not
susceptible to the vagueness of induction.
If the premises are true, and the
deduction logical, then the conclusion is
true.
Example: Socrates is an Athenians. All
Athenians are Greek. Therefore, Socrates
is a Greek.