What is an ideal/physical entity? How far can you indulge in a form of realism before your idealism becomes nearly synonymous to physicalism (depending on the definition)? — substantivalism

The issues that arise come when you define what the terms physical or ideal even mean as either may end in tautologies or an in flux of metaphysical presumptions. When defining what it means for something to be physical we usually start off with our intuitions surrounding everyday objects or waking experiences contrasted to perceptual illusions/our imagination which don't contain the same concrete nature those other things possess. This strategy of playing to our intuitions or talking about what isn't a physical thing (via negativa) isn't all that fruitful and sooner or later a more specific generalized as well as rigorous definition is required. This has lead some to say that what a physical thing is has something to do with our best scientific theories leading to us postulating entities that may be overwritten by future theories or talking about entities in potential theories which don't yet exist (Hempel's Dilemma). In fact it's rather intriguing that the notion of physicalism/materialism has changed in such a large way from being a specific pet ontological assumption about what makes up reality (Lucretius, Descartes, Newton, with their ethers or atoms) to what ever entities happen to be indispensable to a specific scientific theory.

What are your own thoughts on this? — substantivalism

First there was a distinction between what you considered to be part of your mind and what gives rise to said experiences/the nature of these experiences. You don't need to assume here a jump to a form of external realism but merely state via a form of skepticism that we do not truly understand nor could know the true nature of these ideal experiences fully. Idealists attempt to make these things you experience axiomatic/fundamental basically closing off any further investigation of what makes them what they are while a materialist asserts their are things distinct from these experiences you possess that some how metaphysically ground/sufficiently explain their existence/natures but have distinguishable natures of their own. — substantivalism

You can't expect definitive answers to your questions. Remember that we are in the philosophical field.

Anyway, my answer:

Two types of materialism are often proposed: metaphysical and epistemological. My option is different --although close to the second-- : I defend a materialism without matter. My definition of materialism is based on Wittgenstein's familiy-resemblance. A semantic perspective, at least.
I suggest abandoning the search for something called "matter" and focusing on this question:
What is called "materialism" in the different branches of knowledge?

This leads to energy and mass in physics; to biochemical processes in biology; to the brain and behavior in psychology; to productive forces in history; to empiricism in epistemology.

All these options are similar in that they are opposed to supernatural: God, the spirit, the ideal. In short, materialism is the thesis of a unique world at hand. — David Mo

I don't think we need to break our heads on the definition of "physical". Only recognize that thoughts aren't the same as, say, a pencil or a tree. No matter, how one defines "physical" or its antithesis "immaterial" we won't have a good enough reason to put thoughts in the same category of pencils or trees or brains. That's what I think anyway. What say you? — TheMadFool

The way that the traditional philosophers conceived it was that 'the ideal' was not an experience, as such, but what was 'grasped by the intellect' (where 'intellect' is a translation of the Greek 'nous'.) So in the idealist tradition, the form, idea, or essence of a particular was what made something what it is, and the intellect/nous was what enabled the rational mind to understand the forms, and therefore see the essence of things - to see what things truly are. — Wayfarer

Oh, and one more point. The meaning of ‘substance’ in philosophy is quite different to its meaning in ordinary language. ‘Substatia’ was the Latin term chosen by translators for Aristotle’s ‘ouisia’, a word which in many respects is much nearer to our ‘being’ than ‘stuff’. A ‘substance’ was ‘that in which attributes inhere’ - a classic example being that Socrates is an instance of the substance Man, whose eyes happen to be blue. So ‘being a man’ is the substance, and blueness of the eyes is an attribute. — Wayfarer

So are our experiences of the tree and imagined version of the tree completely different substances? That the difference in experience we possess with them warrants a rather significant distinguishing of their natures? — substantivalism

Intriguing perspective. . . I wouldn't have thought to dive right into the semantic end but here we are. I've been more interested as of late into process philosophy which deals with this substance disagreement by dissolving it rather robustly. You on the other hand consider semantic considerations first which is a fairly wonderful take on this. — substantivalism

In fact it's rather intriguing that the notion of physicalism/materialism has changed in such a large way from being a specific pet ontological assumption about what makes up reality (Lucretius, Descartes, Newton, with their ethers or atoms) to what ever entities happen to be indispensable to a specific scientific theory — substantivalism

Atomism - pre-Hobbes, Gassendi, La Mettrie, d'Holbach, Feuerbach "materialism" - includes 'void' as well as 'atoms'. — 180 Proof

I've always interpreted the combinatorial aspect of 'Swirling & Swerving-Atoms-In/(Of?)-Void' as information, or the 'physical measure' of the information content of whatever (i.e. comes-to-be, or continues-to-be, or ceases-to-be) happens. — 180 Proof

Methodological, not metaphysical, materialism no doubt is the worst, least true, intellectual commitment made in human cultural history, except, of course, for all the others tried so far in the last three plus millennia vis-à-vis progressively disclosing how the world (which includes subjects-in-the-world ... as opposed to shibboleth "rational subjects" or "transcendental egos" or "immaterial souls" etc) works. — 180 Proof

Methological, not metaphysical, materialism no doubt is the worst, least true, intellectual commitment made in human cultural history, — 180 Proof

Do you can explain this, please?What "methological" is and why is the worst? — David Mo

... democracy is the worst form of Government except for all those other forms that have been tried from time to time ...

... democracy is the worst form of Government except for all those other forms that have been tried from time to time ...

... panpsychism is the worst theory of consciousness except for all those other theories that have been tried from time to time ...

but how would they know (those philosophers) — substantivalism

paraphrasing Churchill's ironic remark — 180 Proof