Do you agree that physicalism/materialism does not add unknown entities, unlike idealism ?
One thing that has become apparent in reading this topic is that many (not all) materialist skeptics neither understand materialism nor the definition of skepticism and that they tend to beg the question by failing to recognise that their position includes the assumption that material reality is exclusively a property of a materialist universe while anything in consciousness is not reality. You might as well assume that God exists and then start an argument about whether God exists.
Taking the most skeptical position, the one with no assumptions, the only thing which an individual can know is that they are experiencing. Everything else is assumption, including matter.
The materialist says that all our experience of seeing, hearing, tasting, smelling or touching happens inside our heads, that all of those sensations are produced by the brain and that there is a real, material world outside our heads, where the sensations themselves do not exist, and which we can only know through the medium of our senses since we are trapped inside our brain. She says that there is no other way to know that world. In other words, the materialist ASSUMES a real world outside the scope of anyone’s experience as an individual self and that our impression of it relies on the fidelity of our senses (considering this is where thought experiments like The Matrix films originate). Further she ASSUMES that the experience of any individual self is a product of the assumed real world. Note this: materialism imagines that the one thing we can know is the product of something we can only imagine.
Let's be clear. These ASSUMPTIONS are components of the materialist position which comprise an imaginative leap beyond the single knowable fact of individual experience. To label them any more real than the contents of a dream, without question, is a failure of skepticism.
Furthermore, I keep seeing the assertion than an Idealist denies that reality exists. This is a straw man argument. It probably originates with some materialists' unrecognised primary assumptions above. No idealist claims that reality doesn't exist, they simply suppose that reality exists inside consciousness.
Unless we are lucid dreamers we don’t know we are dreaming until we wake up. While we are inside a dream, which exists inside our mind, it’s totally real to us no matter how bizarre. Then how do we distinguish dreams from reality? We identify two things which we say characterise the real world: 1) there are *others who we ASSUME have a similar experience to us; 2) most of the shared experience is not under our individual volition. As far as I can tell, most materialists’ rejection of idealism hinges on these 2 points.
The second of those is not as great as we imagine. Everyone is familiar with what a nightmare is: a dream which isn't going the way you want it to go. We would not suggest that nightmares are under our volition and yet we can accept that they exist entirely within our own individual consciousness. In other words, the absence of volition is not proof that something occurs outside individual consciousness.
Both materialism and idealism assume that others are having a similar experience to our own but they have different ways to view it: materialists suppose that we are separate instances of consciousness experiencing the material world in which we exist, idealists suppose that we are foci of a single consciousness in which the material world exists. A materialist’s mind is inside her head, an idealist’s head is inside her mind.
*(As an aside, does anyone recall whether, in their own dreams, they thought other people were, like their own dream character, having a conscious experience? If so, I’d suggest that there is nothing at all to distinguish ‘dreams’ from ‘reality’. If so, I’d suggest that your dream experience demonstrates that you can participate as an individual with other apparently similar individuals in an ostensible reality all of which is being created inside your own mind).