# Transcendental argument for the existence of God

The Transcendental Argument for the existence of God (TAG) is an argument that attempts to prove the existence of God by appealing to the necessary conditions for the possibility of experience and knowledge.
A version was formulated by Immanuel Kant in his 1763 work The Only Possible Argument in Support of a Demonstration of the Existence of God. C. S. Lewis's argument from reason is also a kind of transcendental argument.
Most contemporary formulations of a transcendental argument for God have been developed within the framework of Christian presuppositional apologetics and the likes of Cornelius Van Til and Greg Bahnsen.

## Transcendental reasoning

"Transcendental" in this case is used as an adjective specifying a specific kind of argument, and not a noun. Transcendental arguments should not be confused with arguments for the existence of something transcendent. Rather, transcendental arguments are arguments that make inferences from the ability to think and experience.
So-called progressive transcendental arguments begin with an apparently indubitable and universally accepted statement about people's experiences of the world. They use this to make substantive knowledge-claims about the world, e.g., that it is causally and spatiotemporally related. They start with what is left at the end of the skeptic's process of doubting.
Progressive transcendental arguments take the form of modus ponens with modal operators:
    If possibly P, then necessarily Q.
    Actually P.
    Therefore, necessarily Q.
Regressive transcendental arguments, on the other hand, begin at the same point as the skeptic, e.g., the fact that we have experience of a causal and spatiotemporal world, and show that certain notions are implicit in our conceptions of such experience. Regressive transcendental arguments are more conservative in that they do not purport to make substantive ontological claims about the world.
Regressive transcendental arguments take the form of modus tollens with modal operators:
    If possibly P, then necessarily Q.
    Actually not Q.
    Therefore, necessarily not P.
They are also sometimes said to be distinct from standard deductive and inductive forms of reasoning, although this has been disputed, for instance by Anthony Genova and Graham Bird.

## The argument

There are many versions of the transcendental argument for the existence of God (both progressive and regressive), but they generally proceed as follows:
* If there is a transcendental unity of apperception, God exists.
* There is a transcendental unity of apperception.
* Therefore, God exists.
The transcendental unity of apperception refers to the combination of different impressions, experiences and categories into a single, intelligible consciousness held by a person. It is argued that the negation of the existence of God therefore entails the impossibility of knowledge, which is self-refuting.
The TAG differs from thomistic and evidentialist arguments, which presuppose the validity of human perception and judgement when proving the existence of God.

## Ash'ari

Medieval Ash'ari Islamic theologians formulated a type of transcendental argument based on the notion that morality, logic, etc. cannot be fully understood apart from revelation and thereby, belief in the Quran and the Islamic truth claims were necessary in order to interpret the external world. For al-Ashari and others, it does not make sense to argue against religion using a priori assumptions about morality or scientific probabilities when these can only be understood in light of divine revelation.

## Criticism

Barry Stroud has criticized transcendental arguments, distinguishing between epistemic (what we must presuppose) and metaphysical (what actually exists) transcendental arguments. Stroud argues that transcendental arguments often only establish the former but assert the latter, so TAG, as a metaphysical transcendental argument, can only establish that human thought presupposes logic, science, and morality, but attempting to ground them in something beyond human thought, such as God, ultimately fails.

### Presuppositional apologetics

Internet Infidels co-founder Jeffery Jay Lowder has argued that the presuppositional apologetics' version of TAG is fatally flawed for numerous reasons. First, Bahnsen fails to defend the necessity of Christianity instead of the mere sufficiency for the rational justification of the laws of logic, the laws of science, and the laws of morality. In other words, such reasoning affirms the consequent. Second, Bahnsen conflates "atheism" with "materialism" and has really presented an argument against materialism, not an argument for Christianity. Third, Bahnsen believed that the laws of logic, laws of science, and laws of morality are abstract objects, but Christianity arguably underdetermines the relationship between God and abstract objects. Some Christian philosophers, such as Peter van Inwagen, affirm Platonism and the compatibility of God and abstract objects. But other Christian philosophers argue that Platonism is incompatible with divine aseity. William Lane Craig urges Christian philosophers to consider anti-realist theories of abstract objects.