Transcript What makes premises acceptable

Chapter 5
Premises: What to Accept
and Why
Important goal: to identify some
general guidelines for what makes
a premise or claim acceptable
7 ways for a premise to be
acceptable
Chapter 5
When premises are acceptable:
Before you begin we need to make an
important philosophical point. Govier refers
to 'acceptable' and 'unacceptable premises.
She doesn't want to refer to 'truth' or 'falsity'
or have you say: 'Such and such is true'
because whether something is 'true' or 'false'
is independent of whether or not anyone
KNOWS or BELIEVES it to be true or false.
Claims: When we take a position on an issue, we assert something or
make a claim. A claim is a statement that is either true or false.
Claims can either be left unsupported or supported. Unsupported
claims are claims for which no verbally expressed reasons for their
acceptance are offered.
When claims come to us with no accompanying reasons it becomes
our job to determine whether there are reasons for accepting or
rejecting them or suspending judgment.
When support is offered for a claim by accompanying reasons we have
an argument (premises + conclusion = argument)
An argument is a set of claims, one of which, known as the principal
claim or conclusion, is supposed to be supported by the rest, called the
premises. The premises are supposed to provide reasons for accepting
the conclusion. The premises attempt to support a claim or assertion
by providing a reason or reasons for accepting it.
Our goal in chapter 5: to develop our ability to
determine whether or not to accept, reject, or
suspend judgment regarding a claim made or
premise presented.
Critical thinking: the careful, deliberate
determination of whether we should accept, reject,
or suspend judgment about a claim and the degree
of confidence with which we accept or reject it.
Emphasis is on rational evaluation and
distinguishing the rational from the rhetorical or
psychological reasons for accepting a claim.
Chapter 5
Premises are acceptable if:
(1) They are supported by a cogent subargument.
This means that if the conclusion of a cogent
subargument is a premise in another argument,
then there is every reason to accept it as a
premises.
Note that it is your obligation to establish that the
subargument passes the ARG conditions.
2) The premises are supported elsewhere.
Elsewhere there could be another cogent
argument that the author or some other author
has already established as cogent. Or the
author may point to external references or
citations that support a point. Keep in mind,
though, that you may have to assess the
credibility of the cited source.
We’ll talk about credibility later.
Chapter 5
(3) The premise is know a priori to be true.
A priori statements are the kind of things a person
could know independent of experience or before
experiences. It is contrasted with the term a posteriori.
Statements that are knowable a posteriori require
experience. Consider the following claims, the first is a
priori and the second a posteriori.
(i)
(ii)
Bachelors are unmarried males.
Chuck D. is a bachelor.
(i) is knowable with out experience, but to know Chuck D. is
a bachelor requires experience in the world.
A priori claims or premises are common in philosophy, logic, and math.
They are not very common in everyday discourse.
Other examples of claims known to be true a priori:
•A=A
• If a = b and b = c, then a = c
• All triangles have three sides.
• The shortest distance between two points is a straight line.
A posteriori claims (known to be true on the basis of experience):
• The earth is round.
• The distance between Pittsburgh and Philadelphia is 305 miles.
• The pyramids were built by ancient Egyptians.
Chapter 5
(4) A premise is acceptable if it is a matter of common
knowledge.
If just about everyone knows or understands that a
premise is true, then the premise is acceptable. Is the
premise widely believed?
Some simple examples:
(i)
(ii)
(iii)
(iv)
(v)
The flu is contagious.
You cannot take a train from London to Los Angeles.
Cats have claws
Motorcycle riders are safer while wearing helmets.
Hitting a curve ball from a Major League pitcher is hard.
Chapter 5
When it comes to common knowledge we have to be
careful because common knowledge can change given
the times and what kind of events are occurring in the
world.
So, must people that live near Chicago, know that the Cubs
last won a World Series in 1908. But few know when the
last time the Los Angeles Dodgers won. If you were
near Los Angeles, you would be more likely to find
someone that knew the Dodger last World Series win
was 1988.
Chapter 5
(5) Testimony -- under some conditions, a claim is
acceptable on the basis of a person’s eyewitness
testimony.
There are three main factors that will undermine our
acceptance of testimony as reliable.
(i)
(ii)
(iii)
The claims made are implausible
The person making the claim or other source is unreliable
The content of the claim goes beyond the experiences or competency of
the testifier
A lot of things give rise to when and how we accept
testimony and how to govern its acceptability.
General Principles in Evaluating Credibility
A list of questions to ask about claims put forward on the sayso of non-expert sources of information:
1.
Did the person have an opportunity to discover or learn
the truth of the matter? If so, how good was the
opportunity?
2. Does the source have the competence or background
knowledge to judge or report about this matter
accurately?
3. Does the information or claim being expressed call for
specialized knowledge or training (expertise)? If so, does
the source have such expertise?
4. Are there excepting conditions in this case which would
call the person’s dependability into question (for example,
pressure, bias, interest, haste)?
Chapter 5
(6) Appeal to a proper authority
Sometimes we have to take the word of a proper authority
with respect to the acceptability of a premise. If a logic
professor told you that a particular argument was
deductively valid, you can trust that because she is a
proper authority on the validity of arguments. This same
logic professor, however, may not be an authority on the
exports of the state of Florida, and cannot explain if an
income tax would increase tax revenue or not.
Authorities must be proper to make premises acceptable.
Evaluating the Credibility of Expert Reports
1. Does the proposition supposedly warranted by expert
testimony belong to an area where expertise is required or
can exist?
2. Does the person appealed to as a credible expert need
credentials? What are those credentials and does the alleged
expert have them? Is that person an expert in the particular
area to which the proposition in question belongs?
3. Has the expert actually conducted an investigation of the
matter on which he or she is making a pronouncement? And
if so, how thorough an investigation?
4. Do different more or less equally authoritative experts
disagree about whether the proposition in question is true or
probable?
5. Are there specific reasons to suspect that the expert
appealed to might not be candid or might unintentionally
mislead?
Chapter 5
(7) The last method of accepting premises is different from
the rest. We say that we accept a premise provisionally
or conditionally.
You might find an argument to pass both the (R) and (G)
conditions for cogency, but are uncertain about the
acceptability of the premises. You can provisionally
accept the premises and thus provisionally accept the
conclusion and cogency of the argument.
Chapter 5
Summary of the acceptability conditions:
A premise in an argument is acceptable if any one of the following conditions is
satisfied:
(1) It is supported by a cogent subargument.
(2) It is supported elsewhere by the arguer or other person, and this fact is
noted.
(3) It is know a priori to be true.
(4) It is a matter of common knowledge.
(5) It is supported by appropriate testimony.
(6) It is supported by an appropriate appeal to authority.
(7) The premise is not know to be rationally acceptable, but can be accepted
provisionally for the purpose of the argument.