Many people, whether or not philosophically well-versed, understandably may not have a firm, unambiguous grasp of what this term means due mainly to its unpopularity in popular social and philosophical vernacular. Metaphysical relativism refers to the belief that there exists no objective truth or reality independent of one's perception. Most people who understand the language employed in explaining this position soon come to realize the self-referential incoherence of holding such a view, which is why most professional philosophers do not endorse this mentality. But that is not to say it is this unpopular in popular culture. I suspect, however, it is only resurfaces as frequently as it does out of a misunderstanding of the terms used to describe it. So let us get started.
In order to understand metaphysical relativism a number of principles and terms must be defined and adequately explained. First, what is meant by the adjective "metaphysical"? Metaphysics refers to concepts relating to the fundamental nature of existence, causality. abstract concepts and their inclusion or exclusion in meaningful philosophical discourse. As such, metaphysical relativism has to do with the philosophy of existence and addresses whether or not objectivities exist. What do I mean by objectivities? This term I think is what causes most of the confusion in pop culture. Many people who are not philosophically well versed do not fully understand what one means when they refer to something such as objective truth. I say this because many secular relativists will speak about arrogance, intellectual pomposity or even social/political authoritarianism when they defend their position. In actuality, however, these things are not logically connected to metaphysical objectivism. All it means is that reality exists independent of one's perception, Inf act, the very word perception is the root of the verb "perceive". What does this imply? It implies objects of perception. If there are objects of perception, then the objects themselves must precede the perception of those objects. Yes, perception can be built upon previous perceptions, but perception itself cannot be the "unmoved mover" so to speak, unless one wants to try to argue for a past-eternal personal history. Therefore, objects of perception must take precedence over perception even if it could be argued that perceptions are merely products of perceptual continuity (due to the principle of causality).
Given these semantic points, the relativist declaration that "reality is perception" is self-defeating given the implications of the word "perceive". Objective reality must exist independent of perception in order for there to be perception., This is not the only sense in which metaphysical relativism is absurd. It also is self-referentially incoherent and tautologically self-defeating. To even say that there is no such thing as objective truth is to implicitly say that no matter what one thinks, there is no such thing as objective truth. But how can this be the case if reality simply IS perception? Metaphysical relativism's logical (to the extent that logic can even wrestle with this junkyard of incoherence) consequence is absolute silence on any matters of fact or even opinion. All conversations within presuppose an objective truth that drives the conversation. All parties are convinced to varying degrees that their view is closer to the truth than perspectives that characterize its opposition. They must believe this to an extent if they have the confidence to contribute their viewpoint to a discussion. To believe anything really presupposes a preceding assumption that there is an external standard of truth that can validate or invalidate beliefs. An assumption of the objectivity of the external world therefore is absolutely and essentially necessary for discussion of any kind to take place. To think otherwise is to embrace chaos.
Most self-proclaimed relativists who take this extreme form of relativism I suspect will readjust their view in light of these semantic clarifications, They need not jettison relativism in every form, but certainly they must give up the notion that reality does not exist external to perception. It is self-referentially incoherent and tries to resist the very fabric of human communication and even human nature itself. Humans are programmed to think in terms of objectivity. Even animals live with an innate assumption that reality exists outside of themselves when they act on their survival instincts. Relativism in this extreme metaphysical form really is the most incoherent, irrational and even life denying philosophy mankind has ever conceived of.