The Cosmological argument A* grade summary notes


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  • Cosmological arguments attempt to show that God exists as the required explanation of the existence of the universe.
  • Aquinas’ 3 ways are 3 varieties of the cosmological argument.
  • A posteriori & inductive argument.

Aquinas’ 1st way (from motion): 

  • We observe that there is motion
  • Nothing moves itself – something only moves when moved by something else
  • There can’t be an infinite regress of movers
  • So, there must have been a first mover that was itself unmoved – that thing we call God.

Aquinas’ 2nd way (from causation):

  • We observe that there is cause and effect in the world
  • Nothing can cause itself – something is only caused when caused by something else.
  • There can’t be an infinite regress of causation.
  • So, there must have been a first cause that itself uncaused – that thing we call God.

Hume’s objection to the causal principle 

  • This especially attacks Aquinas’ 1st and 2nd way. 
  • The causal principle is the claim that every event has a cause. 
  • Aquinas’ 1st and 2nd way clearly assume that this causal principle is true – they assume that everything has a mover or cause.
  • However, Hume casts doubt on that. Firstly he says it cannot be an analytic truth (true by definition).
  • If you deny an analytic truth – you contradict yourself. If you say a triangle has four sides you contradict yourself because the idea of ‘triangle’ is contradicted by the idea of ‘four sides’. So, ‘a triangle has three sides’ is an analytic truth because it cannot be denied without contradiction.
  • But – if you say there could be an event without a cause – this doesn’t seem self-contradictory. The idea of ‘event’ doesn’t seem contradicted by the idea of ‘no cause’. E.g. you could imagine nothingness and then – pop – suddenly something is there without a cause. 
  • So, we cannot know that the causal principle is analytically true – we can’t know it is absolutely true in all cases. It could simply be that every event we have ever observed has a cause – but this doesn’t mean that every event, including the creation of the universe, has a cause.
  • If the universe has no cause – then God can’t be argued for as the required explanation of the causation (or motion) of the universe.
  • Adding modern science to Hume’s point: quantum mechanics


  • What if we accepted Hume’s claim that the causal principle is not an analytic truth, but instead argued that it was a synthetic truth – 
  • The causal principle is an empirical (scientific) hypothesis which has so far been justified by all the evidence we have ever observed. 
  • This makes the causal principle more reasonable to believe in than to not believe in. 
  • So, the cosmological argument would be more reasonable to accept than to not accept. 
  • Maybe we can’t prove the causal principle for absolutely certain as a matter of logic – but so far all the evidence supports it (every time we observe an event, it has a cause) so, arguably we are justified in accepting it.
  • Just accepting that the causal principle is more reasonable to believe that not is enough for the cosmological argument to be convincing, because it is an inductive argument attempting to provide evidence for God, not a deductive argument attempting to provide a logical proof of God.

Optional further evaluation:

  • The fact that every event we observe in the universe has a cause is not even evidence for the universe having a cause.
  • We have no basis on which to think that the conditions within the universe are like the conditions under which the universe came into existence.
  • So, empirical evidence of cause and effect within the universe does not make it reasonable to believe the causal principle.

Aquinas’ 3rd way (from contingency): 

  • The third way involve the terms contingent and necessary
  • A contingent being depends on something else for its existence – it can either exist or not exist.
  • A necessary being does not depend on anything else for its existence – it must exist.
  • There cannot be an infinite regress of contingent beings
  • If everything we see in the universe forms a chain of contingent beings – then ‘before’ this series, there would have been nothing. If everything is on that chain of contingent beings – then before it would have to be nothing.
  • But – how could this chain of contingent beings have come from nothing..? That’s impossible.
  • So, there must be a necessary being which began this series of contingent beings – that thing we call God.


  • Hume’s critique of the idea of a necessary being:
  • A ‘necessary being’ is actually a meaningless concept. 
  • A necessary being is one which must exist. 
  • In that case, we shouldn’t even be able to imagine it not existing. 
  • However, Hume claims that ‘whatever we can imagine existing, we can imagine not existing’. Hume claims we can imagine God not existing – so it must therefore be possible for God to not exist, and this means it cannot be the case that God must exist. 
  • So, the very idea of a necessary being is absurd and meaningless – because there is no being which we are unable to imagine not existing.

Further evaluation

  • The masked man fallacy. 
  • Hume assumes that we cannot imagine impossible things. 
  • The masked man fallacy shows that we can. A person could hear of a bank robbery by a masked man – and they could imagine that it is not their father. However, if it was their father – then it’s impossible for it to not be their father. Yet, that is what they conceived – so, we can conceive of the impossible.
  • In that case, when Hume conceived of God not existing and claimed this meant God’s non-existence was ‘possible’ – Hume was wrong. 
  • God’s non-existence could be an example of something that is conceivable but impossible – as the masked man fallacy illustrates.

The issue of the infinite regress

  • All cosmological arguments rely on the premise that an infinite regress is impossible. 
  • This is because if the universe has always existed (in some form) then God’s existence cannot be argued for as the required explanation of the creation of the universe, since then it would not have been created – it would have just always existed.
  • Perhaps the universe has just always been here, in which case God didn’t cause it.
  • Hume argues that an infinite regress is possible. For something to be impossible, it has to be self-contradictory. The idea of events/things doesn’t seem contradicted by the idea that they go back in time forever. So, it seems possible for things to go back in time forever. 
  • Adding modern science to Hume’s point: E.g. Maybe the universe has been expanding and then crunching forever.
  • So, the cosmological argument rests on an assumption.


  • W. L. Craig defended the cosmological argument from this criticism, using ‘Hilbert’s Hotel’ – a hotel with an infinite number of rooms that are all full. A person shows up wanting a room, so reception puts everyone into their room number plus one. This makes room number 1 free. Then an infinite number of people show up to the hotel – but this is also no problem, since the receptionist can just put everyone into the room twice the number of their current room. This makes an infinite number of odd-numbered rooms free.
  • Craigs point about this – is that surely such a Hotel could never actually exist in reality. It’s absurd to think that infinities could actually exist. If a hotel is full, it can’t make more rooms free – but if it were an infinite hotel – then it could in fact make an infinite number of room free. This just defies all logic regarding how physical reality could actually work. Infinities cannot be possible in reality.

Further evaluation:

  • However, Craig’s argument focuses on the impossibility of an infinity of physical things, but it fails to target the idea of a temporal infinite – an infinite amount of time, which is what the infinite regress requires.

Optional further evaluation:

  • Aquinas has a better argument than Craig.
  • If there were an infinite regress, there would be an infinite amount of time before the present moment.
  • In that case, to get to the present moment, an infinite amount of time would have had to have passed.
  • However, an infinite amount of time cannot pass – no matter how long you wait, it’s not possible to wait for an infinite amount of time.
  • You cannot traverse an infinite through successive addition.
  • So, there cannot be an infinite amount of time before the present moment, and so an infinite regress is not possible.