Organizational Information

1
Organizational Information

• Discussion sections met yesterday, and every
  Wednesday of the semester, henceforth.
• The Power Point presentation from my first
  lecture is now online.
• Course Website http//courses.umass.edu/phil160-p
  graham
• Reading for next time James Rachelss The
  Challenge of Cultural Relativism

2
Arguments

• An argument is a series of propositions meant to
  establish another proposition
• The series of propositions are the arguments
  premises
• The proposition those premises are offered in an
  attempt to establish is the arguments conclusion

3
Validity

• A valid argument is one for which it is
  impossible for all of its premises to be true and
  its conclusion false.
• Another way of putting it a valid arguments
  premises entail its conclusion.
• (The truth of the premises of a valid argument
  guarantee the truth of its conclusion.)

4
Soundness

• An argument is sound if and only if
• it is valid, and
• its premises are actually true.
• Every sound argument has a true conclusion.
• Why?

5
Arguments

• In philosophy we strive to construct valid
  arguments.
• Why?
• If an argument is valid then, to know whether we
  should accept the conclusion we need to determine
  only one thing
• - Are its premises true?
• Why?
• Because if its valid and its premises are true
  then we know that its conclusion must be true.
• And if it is true, clearly we should believe it.

6
Our Focus Valid Arguments

• In this class, when we construct arguments we
  will aim to construct sound arguments (valid
  true premises).
• Also, the philosophers we will be discussing are
  also aiming to construct sound arguments.
• Though there are many different types of valid
  arguments, we will focus on a couple specific
  forms of valid arguments.

7
Modus Ponens

• Some valid arguments are valid merely in virtue
  of their form.
• Any argument with the following form is valid
• P
• If P, then Q
• Therefore, Q
• This argument form is known as modus ponens (MP).

8
Modus Ponens (II)

• Any argument with the following form is also in
  modus ponens form.
• If P, then Q
• P
• Therefore, Q
• The order of the premises does not matter.
• Any argument in modus ponens form is valid. And
  so any argument in modus ponens form that has
  true premises is sound.

9
Modus Ponens (III)

• Five is a number greater than four.
• If five is a number greater than four, then five
  is a number greater than two.
• Therefore, five is a number greater than two.
• If five is a number greater than four, then five
  is a number greater than two.
• Five is a number greater than four.
• Therefore, five is a number greater than two.

10
Modus Tollens

• Here is another valid argument form
• If P, then Q
• It is not the case that Q
• Therefore, it is not the case that P
• This argument form is known as modus tollens
  (MT).
• Just as in the case of modus ponens, the order of
  the premises does not matter.
• Any argument in modus tollens form with true
  premises is sound.

11
Modus Tollens (II)

1. If Barack Obama lives in the Whitehouse, then
   Barack Obama is President.
2. It is not the case that Barack Obama is
   President.
3. Therefore, it is not the case that Barack Obama
   lives in the Whitehouse.

12
Our Focus MP and MT

• In this class we will try to construct arguments
  in MP and MT form
• The arguments of the philosophers we will discuss
  will often be presentable in MP or MT form.

13
Quiz Validity and Soundness

• Can a valid argument have false premises?
• Can a sound argument have false premises?
• Can a valid argument have a false conclusion?
• Can a sound argument have a false conclusion?

14
Learning to PEE

• Often in this class we will, and you will be
  asked to, PEE.
• We will, and sometimes you will be asked to
  Present, Explain, and Evaluate an argument.

15
PEEing

• Story Bert and Ernie
• If Bert is in the bar, then Bert has his ID.
• It is not the case that Bert has his ID.
• Therefore, it is not the case that Bert is in the
  bar.

16
PEEing (II)

• Story Ted Haggards sermon
• God says that homosexuality is wrong.
• If God says that homosexuality is wrong, then
  homosexuality is wrong.
• Therefore, homosexuality is wrong.

17
Normative Ethics of Behavior

• The fundamental project of the normative ethics
  of behavior is the attempt to discover, properly
  formulate, and defend a criterion of moral
  permissibility for act tokens.

18
Types and Tokens

• An act type is a kind of action something that
  can be performed by different people at different
  times and places
• An act token is particular concrete individual
  action something that is performed by just one
  person (the agent of that action), on one
  occasion, and in one place.

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Some Crucial Moral Concepts

• A act token, x, is morally permissible if and
  only if it is morally OK (or morally allowed, or
  morally all right, etc.) to perform x.
• The notion of moral permissibility will be our
  primary moral notion. It is the notion in terms
  of which a number of other moral notions will be
  defined.

20
More Moral Concepts

• An act token, x, is morally impermissible def.
  it would not be morally permissible to perform x.
• An act token, x, is morally wrong def. it would
  not be morally permissible to perform x.
• An act token, x, is morally wrong if and only if
  x is morally impermissible.

21
Even More Moral Concepts

• An act token, x, is morally obligatory def. it
  would not be morally permissible to fail to
  perform x.
• An act token, x, is morally required def. it
  would not be morally permissible to fail to
  perform x.
• An act token, x, is morally obligatory if and
  only if x is morally required.