PHIL 101 Lecture Notes - Lecture 6: Ontological Argument
● Cosmological, Teleological, and Ontological arguments
● The ontological argument is from the Middle ages
● Saint Anselm of Canterbury
● Something than which nothing greater can be conceived
The Argument
1. God is a being of which nothing greater can be conceived (def)
2. It is greater to exist than to not exist
3. God exists in the mind alone, or in the mind and in reality.
4. If God existed only in the mind, then it would be possible to conceive of a being greater
than God.
5. Therefore, God exists not only in the mind, but also in reality.
● This is a contradiction, and therefore God cannot exist only in the mind.
“If it were to exist just in the understanding, we would conceive it to exist in reality too, in
which case it would be greater.” - Anselm
● Some significant philosophers and scientists are followers of the ontological argument
Modern Version of the Argument
1. God exists if and only if God necessarily exists.
2. It is possible that God exists
3. It is possible that God necessarily exists
4. God exists (by standard Modal logic)
Modal Logic
● The logical behavior of modal terms
● S5 logic - most widely accepted today
○ Ex. It is necessary that P = true in every possible world (scenario)
○ It is possible that P = true in at least one possible possible world (scenario)
● What do you do if you put necessity and possibility together?
● It is possible that it is necessary that P =
If P is necessary, than it applies to all worlds, but it is possible that P is not necessary, in which
case it applies to no worlds.
● Every world is accessible from world A (the assumption)
Necessaril
y P
P
P
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Document Summary
The ontological argument is from the middle ages. Something than which nothing greater can be conceived. This is a contradiction, and therefore god cannot exist only in the mind. If it were to exist just in the understanding, we would conceive it to exist in reality too, in which case it would be greater. - anselm. Some significant philosophers and scientists are followers of the ontological argument. Modern version of the argument: god exists if and only if god necessarily exists, it is possible that god exists, it is possible that god necessarily exists, god exists (by standard modal logic) S5 logic - most widely accepted today. It is necessary that p = true in every possible world (scenario) It is possible that p = true in at least one possible possible world (scenario) It is possible that it is necessary that p =
