Chapter 5 PPT Presentation

Chapter 5: Lecture Notes
Premises: What to Accept
and Why
Chapter 5
Acceptable premises are important because even if you
have the best, most elegant reasoning possible, if the
premises are acceptable, then the reasoning does not
What does it mean to say that the premises of an argument
are rationally acceptable? How might we show that they
are? We are going to look at seven ways to show
premises are acceptable.
Chapter 5
When premises are acceptable:
(i) 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. Think about it.
(ii) It is either True or False that there is someone named Deanna sitting in a
Cafe' in Graz Austria right now. But is this reasonable to believe? How can
you KNOW it if you aren't there right now? Or how about whether there is
life after death? It's either true or false, but how do we determine which it is?
Acceptability is a much better concept to start with since it puts this more
epistemologically complex concept of 'what is truth?‘ aside for now
("epistemology" is a branch of philosophy dealing with different theories of
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
(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.
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(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.
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.
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(4) A premise is acceptable if it is a matter of common
If just about everyone knows or understands that a premise
is true, then the premise is acceptable.
Some simple examples:
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
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.
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(5) Testimony -- under some conditions, a claim is
acceptable on the basis of a person’s testimony.
There are three main factors that will undermine our
acceptance of testimony as reliable.
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.
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.
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(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
(1) It is supported by a cogent subargument.
(2) It is supported elsewhere by the arguer or other person, and this fact is
(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.
Chapter 5
When premises are unacceptable:
Premises are not acceptable or unacceptable in many
ways, and we are going to look at five general ways.
(1) The premise is easily refuted. For example:
Every male golfer is better than every female golfer.
All politicians are corrupt.
Both (i) and (ii) are easily show false. Michelle Wie
defeated lots of men in a golf tournament. Abraham
Lincoln or some other politician are not corrupt.
Chapter 5
(2) Claims that know a priori to be false.
There are some statements that are know to be false by
the very understanding. For example,
(i) The triangle did not have three sides.
(ii) The square was not a rectangle.
(iii) He was both awake and asleep at the same time.
All of these statements are false and are know to be false
without having to have any experience. We can reason
that they cannot be true by their very nature.
Chapter 5
(3) Inconsistent premises make the premises
If the premises of an argument directly or indirectly
contradict each other then one of them is unacceptable.
Imagine that in the course of a long argument the
following two statements are made:
James is always mean to Judy.
James kindly helped Judy with her logic homework.
Now it is clear that if (ii) is true, then (i) is false. This kind of
contradiction is implicit because we don’t have a claim
and its direct opposite like: James is not always mean
to Judy, which would be a direct contradiction.
Chapter 5
(4) Vagueness or ambiguity can give rise to unacceptable
premises. For example,
(a) Aggressive behavior is rampant in young boys.
The fact is that the terms aggressive behavior, rampant,
and young are vague and make it so that this premise is
not acceptable in its current form.
In order for us to accept a premise it has to be presented
with clear language that is neither vague nor
Chapter 5
(5) The fallacy of begging the question occurs when the
premises are no more acceptable than the conclusion.
Sometimes this is referred to as circular reasoning or
To beg the question in the logical sense occurs when a
premises is not acceptable because it states or assumes
the conclusion.
The following argument begs the question:
The killing of innocents is wrong.
Abortion is the killing of innocents.
Therefore, abortion is wrong.
Chapter 5
The reason it begs the question is because the first two
premises are in need of support in the same way that the
conclusion does.
In political contexts begging the question means to avoid a
topic or question. This is not the sense for which we are
using begging the question.
Chapter 5
Summary of Unacceptable Conditions
(1) One or more premises are refutable on the basis of common knowledge, a
priori knowledge, or reliable knowledge from testimony or authority.
(2) One or more premises are a priori false.
(3) Several premises, taken together, produce a contradiction, so that the
premises are explicitly or implicitly inconsistent.
(4) One or more premises are vague or ambiguous to such an extent that it is
not possible to determine what sort of evidence would establish them as
acceptable or unacceptable.
(5) One or more premises would not be rationally acceptable to any person
who did not already accept the conclusions. In this case, the argument
begs the question or is circular.
Chapter 5
Internet sources:
When accessing the internet for information you should
keep the following three questions in mind.
What questions are you asking and what is relevant to your search
Which sources are credible and which are not
How to evaluate content and synthesize so as to construct your own
It is important to understand the kind of internet pages you
might encounter: New pages, informational pages,
advocacy pages, business pages, entertainment pages,
and personal web pages all require.
Chapter 5
The credibility of the source is important. Asking these
questions is important.
Who wrote the material?
What are the qualifications of the person?
With what institution or group, if any, is the person affiliated?
If there is an institution or group, what is its nature or credibility?
Is there information that would enable you to contact this author
and make inquiries about the material?
(6) Does this person give sources for his or her claims?
Chapter 5
Dating of Material:
Here are some problems with data from the internet:
(1) Overabundance
(2) Absence of gatekeepers
(3) Mixing contexts
(4) Instability
(5) Confusing mixtures
Chapter 5
Terms to review:
A priori statement
A posterior statement
Begging the question
Common knowledge
Faulty appeal to authority
Provisional acceptance of conclusion
Provisional acceptance of premises

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