The impenetrability of the mind-body problem opens the door to a monism: a unicity which deceptively fronts the duality which we experience. There are 2 basic schools of monism: matterism, where matter defines existence, and energyism, where a unified Ĉonsciousness begets the mirage of a material world. (The term Ĉonsciousness (with a capital ‘Ĉ’) signifies the unified field of Consciousness. The term consciousness (with a lowercase ‘c’) indicates individual consciousness (of any life constituent, including biomolecules, organelles, cells, organs, and organisms).)
The body and mind are not separate. ~ American cognitive scientist Candace Pert
Without duality, there is no mind-body interface. Reality is a unicity. The crucial issue with a monism is explaining how the duality of actuality diverges from a unified reality.
Monism faces the opposite dilemma of dualism, which must integrate the mind and body (hence its failure). A monistic paradigm must account for the duality which is so plain to see. This makes monism difficult to comprehend, particularly energyism, which posits that the physical world is only a proximate subjective experience, and ultimately illusory.
In contrast to energyism, matterism – that the physical is real, and that the mind is a figment created by the brain or other physical substrate – is easier to believe. Newton placed his faith in empirical matterism, as would later physicists and other scientists in his esteemed wake. If nothing else, it seemed a solid bet.
Matterism is a reasonable castle built on rotten foundations. ~ Dutch philosopher Bernardo Kastrup
The more philosophically inclined – Leibniz, Berkeley and Kant, among others – viewed materiality as delusory. This stance acts as a springboard to explain the grand illusion of physical existence; something early proponents could not convincingly do, as scientific knowledge had not progressed far enough to posit an evidentiary basis for energyism. Anyway, explaining away what is apparently there is an almost insurmountable obstacle. Hence, natural philosophers on the right track lost out to empirical science.
Having conducted decisive studies of mass and motion, and contemplated a heretical place for Earth among the heavens, Italian physicist Galileo Galilei was a central figure in transitioning thought in a material direction, with matter bound by mathematical laws. Its appeal was that it seemed so tidy as to make the wonders of Nature comprehensible. This sanguine frame of mind inspired the Age of Enlightenment and Scientific Revolution: that man was making progress.
Inspired by Galileo, French friar Marin Mersenne, a contemporary of Descartes, fought to fend off Renaissance animists: those who believed that the spiritual world existed within the material one. Mersenne sought to draw a categorical distinction between the material world and immortal souls, a line being blurred or outright denied by Enlightenment thinkers. Mersenne found his answer within the emerging new philosophy: Nature could be conceived as a grand machine, something which souls could never be confused with.
Mersenne’s enthusiasm in promoting this idea proved a pyric victory. Mechanics came to dominate the paradigm of science. The soul was scorched off, leaving only a material world, where bodily death spelled oblivion.
The sciences hold each other by the hand, so that they follow one another in a natural order. ~ Marin Mersenne