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I want to ask "what is the difference between the physical or material and the non-physical or non-material?" Everything that exists must be composed of some substance. I remember from a particular philosophy book that there used to be a debate about what everything is made of. The question asked: "what is the substance of existence?" There were two schools of thought 1. idealism, 2. materialism. I understand Plato was the representative of the first: all that really (ultimately, without-end) exists is "idea," or "mind," or "spirit." According to Plato (student of Socrates) the physical world existed after the non-physical "ideal" world and was fashioned after it's likeness in an attempt to redeem it, like the Gnostic demiurge modeled chaos into the form of things in the Aeon (world) above. Plato taught a morality based on self-denial and obedience to enlightened philosopher kings in a perfect "Republic" based on an order above. Aristotle (student of Plato) represented the second view: all that exists is matter, what is physical. God, the "nous" or "mind" that created physical creatures exists out somewhere, and is a superior being (like a man) who has no concern for humans and this world. Aristotelian ethics is about developing what is within the self most fully, mostly finding one's place in society and being kind to fellow men. Death means death and no reward or punishment is promised in Aristotle's philosophy, just like the Epicureans who saw creation as the result of colliding atoms in space and life as the quest for earthly contentedness. In contrast you have the school of Xeno and the Stoics, who stressed moral living and the existence of a divine being who placed a living soul: "fire" or "ether" within each human being and created the four material elements which make up the physical world. In the end most people agreed on the existence of 2 kinds of substance, except atheists, who see matter as all that exists, and Brahmans & Buddhists who view all matter as "maya" or illusion and spirit as the only reality. But what is the difference between the 2 substances? Benedict Spinoza, an outcast Jew from Holland, posited the existence of a third substance that makes up both matter and spirit. This third substance is God, and everything is a manifestation of God.
As I understand it, there are four schools of thought here, not just materialism and idealism, that is, that all of reality is made of one substance - matter in the first case, from which mind emerges as an epiphenomon (think Hobbes), and mind is the fundamental reality in the second, from which matter (or the experience of matter) is derived (think Berkeley).
You alluded to the third monistic possibility with your reference to Spinoza, neutral monism, which posits that both mind and matter are derivative and arise as different manifestations of a more fundamental substance unseen to us. We don't need to call this "God." A substance need not be conscious to fulfill this role.
The fourth position isn't a form of monism at all, but so-called Cartesian dualism. Descartes called mind and matter radically different and unrelated substances that are somehow coordinated, his solution to the mind-body problem..
There is no way to decide among these four. They are all logically possible, and none of them can be ruled in or out. We tend to have preferences - I like neutral monism - but they are merely unsupportable hunches or intuitions. I can't support my preference, or even explain why it is my preference.
Given that, the only defensible position one can take is agnosticism, or the suspension of judgment about an undecidable proposition.
To bring this back to the OP, material monism is essentially synonymous with physicalism, or more properly philosophical physicalism, and both are essentially synonymous with materialism, which is an unfortunate and dated term arising from a time when it was thought that all reality was matter (atoms) and empty space. Once energy and then force/force fields were elucidated, the term became obsolete and was upgraded to physicalism, which the idea that matter,energy, force, space and time are the elements of reality..
The term philoshical physicalism exists to distinguish the metaphysical position that physical reality is all that there is, or underlies all that there is, from methodological physicalism, which isn't a philosophy at all, but the acknowledgement that the physical realm is all that is accessible to our inquiries into the nature of reality whether there be more than the physical or not.
And now to answer the OP: There is no evidence for (philosophical) physicalism.
There is evidence of the physical, but not that that is all that there is, or that the physical is the fundamental reality, that is, that it isn't derivative from mind or a neutral precursor to mind and matter. Asserting otherwise is making a claim to knowledge that one cannot possibly have - a condition called faith, as when one asserts that a god exists rather than using words like "seems likely" or "I believe."
As stated earlier, the logically defensible position regarding the nature of the fundamental substance or substances comprising reality is agnosticism, not (philosophical) physicalism.
Most of us rational skeptics are empiricists, an epistemological position, but not physicalism, which is a metaphysical position. That may be why 1137 has been having difficulty getting anybody take the position for which he wants somebody to offer evidence in defense.
