3. Ontological Arguments: Attempt to give a priori arguments for the
existence of God
A Priori Proposition: If it can be justified independently of sense experience
(reason is sufficient to know its truth and justify it.) Theoretical deduction.
1+1=2; bachelors are unmarried
A Posteriori Proposition: If it can only be justified or known through information
and observation from the senses
Bachelors eat mac and cheese
Anslem’s Ontological Argument:
P1: God is by definition the greatest being possible.
P2: A being that fails to exist in the actual world (while existing in other
possible worlds) is less perfect than a being that exists in all possible
C: Hence, God exists, necessarily.
“… if it can’t exist, it can’t be the greatest conceivable. It must exist”
Necessary Truth: A statement that is true in all possible worlds. 1+1=2
Contingent Truth: A statement that is only true in certain worlds. I came to class
P1: A P-island is by definition the greatest possible island.
P2: An island that fails to exist in the actual world (while existing in other
possible worlds) is less perfect than an island that exists in all possible
C: Hence, a P-island exists necessarily.
A form of Reductio Ad Absurdum… (Modus Tollens) P1: If Anselm’s argument is sound, than my perfect island argument is
P2: My P-island argument is not sound; it’s absurd
C: Anselm’s ontological argument is unsound.
Anslem’s Response to Gaunilo: The E- Unicorn Analogy
Unicorns don’t exist in the actual world, but consider a new concept that we can
call an E-unicorn. An E-unicorn is by definition an existing unicorn … so, are
He simply says if there was an E-unicorn, it would have that property of
existing; similarly, Anslem is saying that if God existed, he would be the
Expected Utility: Expected magnitude of satisfaction to your preferences
Expected Value of Outcome: (Gain * Prob1bility ) + (Ga1n * Proba2ility ) + … 2
Gain Ticket wins (1/1 million) Ticket loses (999 999/1 million)
#1 Buy ticket $100 000 - $1
#2 Don’t buy / /
• EV of #1: (100 000) * (1/1 million) + (-1)(999 999/1 million)
EV of #2: 0
To maximize expected monetary value, don’t buy the ticket
Pascal’s Wager: Questioning the evidential and prudential rationality for our
Evidential Rationality: believing only what is given through facts and
information Prudential Rationality: an action that maximizes expected utility
Gain God exists 50% or 1% No God exists 50% or
Believe in God Infinity Finite loss (-x)
Don’t believe in 0, or, – infinity Finite gain (+x)
Objections to Pascal’s Wager:
(1)Many Gods Objection, which states that there could be multiple Gods that
reward different people according to different values.
(2)Maybe God will only reward evidential rationality and punish those who
display prudential rationality.
William James: Gives an argument for the belief in the existence of God based
on rationality of one’s own individual psyche, focused on present day beliefs as
opposed to after-life circumstances.
Gain Reassured by theism Not reassured by theism
Believe God exists +x -x