Ontological argument
1. God is, by definition, the greatest conceivable
being.
2. God exists at least in the understanding (we
understand this definition).
3. A God that existed in reality would be better
than one that existed merely in the
understanding
4. Suppose that God doesn’t exist in reality, but
only in the understanding
5. Then we could conceive of a being greater
than God, namely a real God (from 3)
6. But then we could conceive of something
greater than the greatest conceivable being
(from 1)
7. Since that is a contradiction, the
supposition (4) must be false
8. Therefore God exists in reality as well as the
understanding. I.e., God exists.
Rough idea: existence is an essential part of
God’s nature. God couldn’t not exist, any more
than a bachelor could be married (and still a
bachelor) or a triangle be four-sided.
Problems with the ontological argument:
Gaunilo’s objection:
Something must be wrong, because it “proves”
too much: a perfect island
Not that anything you can imagine exists, only
absolutely perfect things
Kant’s objection:
Existence is not a predicate
(i.e., it is not a quality that changes the nature of
something)
If existence is not a quality, it cannot be a
quality that increases greatness
Blackburn’s objection:
Real and imagined things are incommensurable
Do imaginary turkeys weigh more or less than
real ones?
Both attack premise 3
Ontological argument is a priori: it relies on
reason alone, rather than experience. In this way,
like mathematics, unlike science
Other arguments are a posteriori: they rely on
experience
Perhaps the existence of God is like the
existence of leptons, quarks. These are things we
posit in order to make sense of observations
Cosmological Argument:
The very existence of the world indicates that
God exists
Argument from (to) Design:
The perfect nature of the world indicates that
God exists
Cosmological argument
1. Everything that exists has a cause or reason
for its existence. (Principle of Sufficient
Reason)
2. All worldly beings are dependent beings, i.e.,
they depend on something else for their
existence.
3. Furthermore, the whole chain of worldly
beings, even if infinite, is itself a dependent
being.
4. There must be something that explains the
whole chain.
5. But it cannot be a dependent being, for all of
these are already included in the chain.
6. Therefore, there must be a necessary being,
i.e., one whose nature explains its own
existence.
Hume’s objection:
God does not seem to be a necessary being. We
can imagine God not existing.
If God is not necessary, then his existence only
pushes things back a small step; it raises more
questions than it answers
One might reply:
“But maybe God is necessary despite his not
seeming so”
Maybe, but then the same could be said about
the world.
Our reason for thinking that the world needs
something else to explain it applies to God as
well: we can conceive of it being otherwise.
If that’s a good reason, then the cosmological
argument fails, and if it’s a bad reason, then the
cosmological argument still fails
Argument from (to) Design
1. The world and many of its parts exhibit
functional complexity (i.e., certain
arrangements of matter are ‘just right’ – a
small change and they would no longer
perform their functions).
 Examples: the human eye, pond ecosystems,
gravitational constant
2. In this respect, the world is like a giant
machine.
3. Like effects have like causes.
4. Machines have intelligent designers
5. Therefore, the world has an intelligent
designer
Hume’s reply:
It’s an argument from analogy, and those are
only as strong as the similarities.
Does the world really resemble a machine?
Does it resemble a perfect machine?
Does it resemble a machine more than it
resembles a plant?
But do we need an intelligent designer to explain
how generation gives rise to order?




Several known sources of order:
Intelligence
Instinct
Vegetation
Generation
There is no reason other than human arrogance
to elevate intelligence above the others, as the
ultimate cause of the rest.
In our experience, we see the order going the
other way around, generation and vegetation
giving rise to intelligence, rather than vice-versa
The Problem of Evil
Traditional theism: God is
 All-powerful
 All-knowing
 All-good
If such a God existed, there would be no evil in
the world.
But there is; therefore, such a God does not
exist
Argument can be read probabilistically: perhaps
there is an all-powerful, all-loving, all-knowing
God, but there is no evidence for that claim and
quite a bit against it
Free-will defense
Evil is the result of human freedom, and a world
with human freedom and human suffering is
better than a world with neither
Blackburn:
This only accounts for some of the evils. It is
doubtful that earthquakes, plagues, etc. are the
result of human free will
Perhaps God is “beyond good and evil”, so
incomprehensible in his infinity that our human
categories can’t apply to Him
Blackburn:
Then theism is worthless, can’t be a guide to
life. The difference between theism, atheism
makes no difference