...of the Brain in a Jar hypothesis (ie. the Matrix theory).
Some may not have been swayed by my discussion of Descartes and the nature of objective reality; they could well claim that even if there is such a reality, it would be beyond the perception of and thus irrelevant to the BiaJ. And quite right they are that such a brain would not experience the objective reality but would instead perceive an entirely subjective reality.
So where does the relevance of objectivity come from? Well, apart from the fact that we could plausibly be brains in jars, what evidence is there AT ALL that this is in fact the case? Similar to the Truth as Opinion post below - just because something is plausible does not make it true. Especially when there is, by definition, not a shred of evidence to support it.
Furthermore, so what if it is ultimately revealed that the world we experience is in fact psychologically engineered? Without the evidence to support such a claim and with it instead wholly pointing towards our perceived reality (remember that this is evidence, not conjecture) as the true one, we should rationally accept that we experience the true reality. It may turn out that the skeptics are right, that the true objective reality is beyond our perception, but we currently have as little reason as they do to believe this is the case. Namely, none.