Each well-known proposed solution to the mind-body problem encounters an impasse. These take the form of an explanatory gap, such as the one between mental and physical, or between micro-subjects and macro-subject. The dialectical pressure to bridge these gaps is generating positions in which consciousness is becoming increasingly foundational. The most recent of these, cosmopsychism, typically casts the entire cosmos as a perspectival subject whose mind grounds those of more limited subjects like ourselves. I review the dialectic from materialism and dualism through to panpsychism, suggesting that explanatory gaps in the latter stem from assuming foundational consciousness to be perspectival. Its renunciation may yield the notion of an aperspectival, universal, “non-dual” consciousness that grounds all manifestation and is unstructured by subject, object or any differentia. Not only is such consciousness suggestive of a natural successor to cosmopsychism, but it has also been reported to be the direct experience of mystics who claim to have transcended the individual perspective. Their purported insight — that our aperspectival conscious nature is identical to the ground of all being — has been termed “the Perennial Philosophy”. Believing this Perennial Philosophy to offer the most promising way forward in the mind-body problem, I construct from it the foundations of a metaphysical system that I call “Perennial Idealism”. This attempts to account for manifestation in terms of dispositional, imagery-bound subjects. I then address an age-old “Parmenidean” conundrum that I refer to as “the problem of the one and the many”: How can an undifferentiated substratum ground differentia without the ground itself differentiating? The proposed solution takes its cue from mystico-philosophical writings in the Advaita Vedānta tradition, known as the ajāta doctrine.