The Munchhausen trilemma is a thought experiment used to demonstrate the theoretical impossibility of justifying any truth without unjustifiably accepting certain axioms. The trilemma posits that there are only three ways of completing a proof:
- Circular argument
- Regressive argument
- Axiomatic argument
The first involves using the conclusion of an argument as a premise. An example of this is: “1+1=2 because 1+1=2”. Clearly, this is unsatisfying as the contrapositive would dictate that this method of reasoning can support any imaginable proposition. The second, regressive arguments, is also unsatisfying, as it results in an infinite regress, where each proof would require further proof, ad infinitum. The third option is most commonly used, yet it assumes the veracity of certain axioms. Instead of defending the precepts, an axiomatic argument merely asserts them to be true. Though Hume's guillotine was initially presented as an argument against moral truths, it can be used here to demonstrate why the axiomatic argument is not satisfying. Seemingly factual statements such as water consists of two parts hydrogen and one part oxygen are established under the assumption that people ought to value things such as evidence, rationality and reason, thus they cannot be objective truth claims.
This invites the search for an indisputable fact which presupposes all knowledge. As Descartes famously declared, cogito ergo sum. The only certain and irrefutable fact is that one’s mind exists, as it is impossible to doubt the mind’s existence, because doing so would entitle that there is a host for the doubter i.e. yourself. This level of certainty, however, does not extend to the external reality. Humans perceive (or so we think) reality through some form of qualia, however there is no reason to believe that they are indicators of an external reality. Whilst we can be certain that our qualia exists within our mind, there is no reason to believe that they provide any insightful tellings of the “real world”.
Thus, the existence of the physical world can be discarded purely on the basis of Occam's razor, which asserts that a theory is more likely if it has lesser ontological commitments than a competing theory. As metaphysical solipsism posits fewers ontological assumptions than any competing theory, it ought to be deemed as that which is most likely to be true.
Contention II: Monistic Idealism
Monistic Idealism is the position that all of reality consists of a single substance, being the mind. Such idealists hold that nothing outside the mind is true, and that the external reality does not exist. The position is defended by the following.
p1. The mind and the non mind are distinct entities.
p2. The mind cannot interact with the non-mind
p3. If p2, it is likely that the non-mind does not exist.
c1. Therefore, it is likely that metaphysical solipsism is true.
The first premise is contingent upon Identity of Indiscernibles, which dictates that no two things have exactly the same properties. As the mind and non-mind are distinct entities, they must also be distinct in terms of their properties.
The cogency of the second premise is affirmed on the grounds of what is known as the Princess Elisabeth attack on Decartes' dualistic theory. The attack dictates that given the mind and non-mind are polar opposites in terms of composition, it is impossible for the two to interact with each other. In particular, Elizabeth employs the following principle:
- When A causes B, there must be some connection by means of which this causal relation occurs.
To assert that the mind and non-mind can communicate would be like declaring that an invisible, intangible, inaudible and undetectable fairy can make changes to the physical world. Clearly, there requires a third substance of which ties the physical and non-physical together, however, there is an absence of evidence for such a substance.
Premise 3 is valid as it has already been demonstrated that the existence of the mind is certain, whilst the non-mind is not. As premise two dictates that the non-mind and mind cannot communicate in any known way and it is known for certain that the mind exists for certain, the non-mind therefore does not exist. Moreover, if the non-mind were to exist, it would not be perceivable by the mind, as this would be analogous to fairies interacting with the physical world.
Thus the conclusion is valid if premise 3 is true. As it has been shown that it is indubitable that the mind exists, whilst it is uncertain that the non-mind exists, the likelihood of metaphysical solipsism logically follows.
Whilst the notion that our qualias can be trusted in constructing an objective reality is often thought of as a plain fact, Descartes dive into skepticism finds that this concept is supported by faulty reasoning. To support this notion, I postulated that metaphysical solipsism is the most preferable ontology in regards to epistemology – this is true due to Occam’s Razor – solipsism is simply the least ontologically committed ontology. Secondly, I imposed the argument from monistic idealism which stipulates that reality consists only of a single substance, being the mind. I professed that it would be logically incoherent for the two to interact with each other and would logically require a third substance to act as a medium for interaction; yet evidence of such doesn’t exist. As such, the likelihood of metaphysical solipsism is entailed from both arguments.