PHIL 112 Lecture Notes - Lecture 8: Modus Ponens, Modus Tollens, Disjunctive Syllogism

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1. Define and understand: “argument,” “valid,” “sound,” “modus ponens,” “multiple modus ponens,”
“disjunctive syllogism,” and “modus Tollens.”
a. Argument
a.i. An argument is a sequence of sentences, the last of which (the conclusion) is supposed
to follow from the others (the premises
a.i.1. Sequence indicates a collection of sentences has a specific order (order
b. Valid
b.i. An argument is valid if its conclusion must be true if its premises are all tore
b.i.1. If an argument is valid, then it is Impossible for premises to be true and the
conclusion to be false
c. Sound
c.i. An argument is sound if it is valid and all of its premises are true
d. Modus ponens
d.i. P
d.ii. If P, then Q
d.iii. Therefore, Q
e. Multiple modus ponens
e.i. P
e.ii. If P, then Q
e.iii. If Q, then R
e.iv. Therefore, R
f. Disjunctive syllogism
f.i. P or Q
f.ii. Not P
f.iii. Therefore, Q
g. Modus Tollens
g.i. If P, then Q
g.ii. Not Q
g.iii. Therefore, not P
2. Present, Explain, and Evaluate Priest’s argument against the Wittgenstein/Derrida account of philosophy.
a. Priests argument against the Wittonstein/ Derrida account of philosophy
a.i. If Wittgenstein/ Derrida view of philosophy is rite then philosophers are not debating
facts about the world
a.i.1. Some of our acts are free
a.ii. But Philosophers are debating about facts about the world
a.ii.1. God exists
a.ii.2. God is all Powerful
a.iii. Therefore the view about philosophy is not right
b. Priests conception pf Philosophy
b.i. Philosophy is the intellectual inquiry in which anything is open to critical challenge.
And in which are evaluates peoples ideas and develops and defends alternative views.
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c. Explain
c.i. Philosphers do not just merely play a word game they try to answer questions about the
world that not everybody neccisarisly agrees on.
d. Evaluate
d.i. Valid
d.i.1. This argument is valid because if all of the premises are true then the
conclusion must be true
d.ii. Format
d.ii.1. Modus Tollens
d.iii. Sound
d.iii.1. This argument is sound because philosophers do debate about facts about
the world and are not just concerned with a word game as the other philosophers
d.iv. My thoughts
d.iv.1. …..
3. State and explain the principles MRF, PUC, and FWT. Give a reason for believing each. Explain why
someone might think PUC and FWT are incompatible.
a. MRF (Morally Responsibly only if Free)
a.i. You are not morally responsible for an act unless you do it freely
a.ii. S preforms A freely means that S performs A but could have done otherwise
a.ii.1. Mind control from the evil scientist (wasn’t actually you’re doing)
b. PUC (Principle of Universal Causation)
b.i. Every event has a cause
b.ii. All science is based on the fact that PUC is true
b.iii. English queen and the commission for the crop circle example
c. FWT (Free will thesis)
c.i. Sometimes we act freely
c.ii. Evidence
c.ii.1. We sometimes do what we choose
c.ii.2. We have the feeling of freedom
d. Why PUC and FWT contradict
d.i. PUC says all events are caused and if this is true there is no way in which we could ever
act freely if everything even our thoughts and emotions are caused by something
4. State and explain Hard Determinism being sure to indicate what HD implies about PUC and FWT and
moral responsibility. Discuss a possible problem for HD. Discuss what you think about HD.
a. Hard determinism states that every event has a cause so no one event or act is every done freely
b. Implications towards FWT
b.i. HD implies that FWT is completely incorrect. If all of our actions are already pre-
determined, then we may never act freely and therefore are never morally responsible
for our actions.
c. Implantations towards PUC
c.i. HD is sort of a spin off and extension of PUC. The idea that every event has a cause is
PUC and HD extends this to the rational that since every act has a cause we are never
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Introduction to Philosophy
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morally responsible for any action that takes place
d. Problems
d.i. Her “I could have done otherwise “
d.ii. Ray- if hard determinism is true then no one is ever morally responsible for what they do
e. My thoughts
e.i. ……….
5. Present, Explain, and Evaluate the Argument against HD based on Moral Responsibility.
a. Argument against HD based on moral responsibility
a.i. We are sometimes morally responsible for what we do
a.i.1. Nobody deserves punishment?
a.i.2. Nobody deserves praise?
a.ii. If were sometimes morally responsible for what we do, then we sometimes act freely
a.iii. 9if we sometimes act freely then Hard Determinism is False
b. Explanation
b.i. This argument basically states that we must be morally responsible for at least some of
the actions that we do because if we are not then people like mass murderers and rapists
are not responsible for their actions and on the other hand this also means that heroes
must not be praised because they had no choice in the matter of their heroic acts.
c. Evaluation
c.i. This argument is valid because if all the premises to the argument are true then the
conclusion must be true
c.ii. The argument is in the format of a multiple modus opens
c.iii. Sound?
c.iii.1. I think this is a sound argument because it is a valid argument and it does
not make sense to accept a theory in which no one holds any moral responsibility
for any of the actions in which they commit.
6. State and explain Radical Indeterminism being sure to indicate what RI implies about PUC, FWT, and
moral responsibility. Discuss a possible problem for RI. Discuss what you think about RI.
a. RI (Radical Indeterminism)
a.i. Free action is seen as an act that has no cause
a.ii. We do sometimes act freely and so some events are uncaused
a.iii. People are morally responsible for their free acts
b. Implications to PUC
b.i. Does not support PUC because it implies that not all acts have causes
c. Implications to FWT
c.i. Supports the Free will theory because it states that people have free will
d. Implications to moral responsibility
d.i. Implies that we do have a moral responsibility to all the acts that are not caused and we
perform under our own free will
e. Possible Problems
e.i. If you’re not caused to do what you do, you can’t be morally responsible for your
actions!! (Leo the Lunatic)
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