Secondly, the cosmological argument is also far from perfect. This argument claims that all things in nature depend on something else for their existence (i.e. are contingent), and that the whole cosmos must therefore itself depend on a being which exists independently or necessarily - God. Some scholars have argued that Aquinas' arguments rest on assumptions that are no longer widely held, such as a hierarchy of causes. Additionally, if nothing can cause itself how can God be seen as an uncaused causer?
Both Hume and Kant criticised the Cosmological Argument. Hume maintained that we have no experience of universes being made and it is simply not possible to argue from causes within the universe to causes of the universe as a whole. There is a logical jump which the argument fails to recognise. It is one thing to talk about causes that operate within the system of the universe, but it is an entirely different matter to speculate about whether the system as a whole is caused.
Kant rejected the argument outright not only because he maintained that the idea of a ‘Necessary Being’ was incoherent but also because our knowledge is limited to the phenomenal world of space and time and it is not possible to speculate about what may or may not exist independently of space and time.
Finally, the ontological argument naturally attracted much criticism from both inside and outside of the church due to its unique and abstract way of thinking. The ontological argument asserts that the very definition of God means he must exist, for you cannot have a greatest possible being that doesn’t exist. Kant’s main criticism of the ontological argument was that he believed existence was not a predicate, as in existence is not a quality an object can have. If this was the case then when people say there is no God, they actually mean there is a God but he lacks the quality of existence. They would be affirming and denying that God exists at the same time, which is a logical fallacy.
The centre of Kant’s philosophy is a concept known as ‘thing-in-itself.’ This does not concern the outward phenomenon, that which deals with empirical recognition, but the object itself, the very substance of the phenomenon’s origin, independent of any subjectivity. Therefore he argues that we can understand a concept, but never truly ‘know’ the object. Therefore even though humans understand the concept of God, it does not mean they can ever claim to know that he exists. Russel and Hume built on these criticisms to claim that existence does not necessarily add anything to an object. For example, an imaginary hundred dollars consists of the same amount of dollars as a real hundred dollars.
Ultimately, a belief in God will always be fundamentally routed in faith rather than philosophy. The arguments critiqued here are inductive, meaning they were intended by the arguer merely to establish or increase the probability of its conclusion (God exists). This is because both Aquinas and Anselm were writing primarily to justify the faith of those that are already theists and did not intent their arguments to convince atheists into conversion.