iii) Idealism and Anti-Realism
iv) Kant's Transcendental Idealism
v) The Copenhagen Interpretation
Donald Hoffman's philosophical position is called conscious realism. He opposes that position to panpsychism and to Kant's transcendental idealism.
In terms of panpsychism: there are clear distinctions between Hoffman's conscious realism and panpsychism. However, there are very clear and strong similarities too. (In one place, Hoffman does say that he accepts what he sees as one type of panpsychism – the one that's not, in his eyes, “dualist”.)
If we turn to Kant.
Hoffman is against Kant's transcendental idealism for the primary reason that he doesn't deem it to be scientific. Nonetheless, his arguments against Kant are neither convincing nor does he distinguish his own position strongly enough from transcendental idealism.
As for anti-realism.
Hoffman hardly mentions it. Nonetheless, he does mention the Copenhagen interpretation of quantum mechanics favourably. In fact he uses it (in various places) in order to defend his own position of conscious realism. The thing is that Hoffman makes the Copenhagen interpretation seem idealist in nature. That said, he's hardly the first person to have done so (see here).
And on the subject of idealism.
This piece argues that Hoffman's conscious realism is a new-fangled take on idealism (i.e., idealism with mathematical and scientific knobs on it). Hoffman will deny this and he'll do so for various reasons. Primarily, Hoffman will do so because he does indeed believe that there's a “reality” out there. (He often uses the word “reality” positively – that there is a reality - many times; despite the fact that he's just written a book called The Case Against Reality.) Nonetheless, Hoffman also argues that we haven't got direct (or even indirect) access to that reality. Instead, we've only got access to the contents of consciousness. And that's still the case even if those contents belong to some kind of collective of consciousnesses (i.e., that of a collective of what Hoffman calls “conscious agents”).
“Conscious realism is not panpsychism, nor does it entail panpsychism.”
Of course it can now be said that even if Hoffman's conscious realism (CR) isn't identical to panpsychism - and also that it doesn't “entail panpsychism”, that still doesn't mean that it has nothing in common with it at all. It may even be the case that Hoffman's conscious realism has a lot in common with panpsychism.
Hoffman then makes various distinctions between his own position of conscious realism and panpsychism. He states:
“Conscious realism, together with MUI [multimodal user interface] theory, claims that tables and chairs are icons in the MUIs of conscious agents, and thus that they are conscious experiences of those agents. It does not claim, nor entail, that tables and chairs are conscious or conscious agents.”
That last sentence is of course directly and clearly aimed at panpsychism. That being said, not many (if any) panpsychists argue that tables and chairs are “conscious agents”. They simply argue that tables and chairs (or their many parts!) are conscious or that they have (whatever that may mean) experience. (More of which in a moment.)
The rest of the Hoffman quote above makes some correct distinctions between panpsychism and conscious realism. For one, panpsychists most certainly don't claim that “tables and chairs are icons in the MUIs of conscious agents”. And neither do they claim that tables and chairs are the “conscious experiences of  agents”. More importantly (unlike conscious realism), panpsychists do claim that “tables and chairs [or their many parts] are conscious”; though they rarely (if ever) claim that they're also “conscious agents”. (This raises the question: What does Hoffman mean by “agent”?)
Of course there are different types of panpsychism and not all panpsychists would be keen on using the precise words “tables and chairs are conscious”. Instead, some panpsychists would say that tables and chairs are made up of entities which contain (or have) “phenonemenal properties/qualities” (or “(proto)phenomenal properties”). This clearly isn't as grand as claiming that tables and chairs are “conscious”. (I don't use the term “qualia” here because that will lead to unclarity.) And it's certainly less grand that claiming that tables and chairs are conscious agents.
However, one part of Hoffman's story does seem to chime in with panpsychism. Take this passage:
“The story that there was first the Big Bang and then, billions of years of later, life, and then, hundreds of millions of years later, consciousness, is fundamentally wrong. It's the other way around. Consciousness is fundamental.”
Most panpsychists would be very happy with Hoffman's sentence above. Nonetheless, although they believe that “consciousness is fundamental”, panpsychists and Hoffman have very different takes on those three words. Put simply. Consciousness is fundamental to panpsychists in the sense that all things have various degrees of consciousness (or experience). To Hoffman, on the other hand, consciousness is fundamental in that the contents of an individual's consciousness (or the contents of various collectives of conscious agents) is literally constitutive of reality or the whole of the universe (as well as everything in it).
Both panpsychists and conscious realists agree that consciousness (or experience) isn't an “emergent property” at all: it's been around since the Big Bang. Thus if consciousness has been with the universe (as it were) since the Beginning, then the issue of the emergence of consciousness becomes a non-problem.
Panpsychists tend to think of consciousness (or phenomenal properties or experience) as being “fundamental” in the sense that it exists all the way down and all the way up. (That is, all the way down to particles and all the way up to human beings.) Hoffman, on the other hand, stresses the fundamentality of consciousness by writing it into the story at the Big Bang (actually, just after). Having said that, these two emphasises work perfectly well together. That is:
i) If we have consciousness all the way down to particles,
ii) then that's precisely because we had particles - and therefore consciousness - (just after) the Big Bang.
Thus these two positions fit perfectly well together.
To repeat. Hoffman's position can be seen as a take on panpsychism in that he states that “consciousness is fundamental”. (Three words which many panpsychists often use together - see here.) Panpsychism also rejects the emergence of consciousness from the physical and stresses, instead, that it's not the case that (to use Hoffman's words) it's “a latecomer in the evolutionary history of the universe” that “aris[es] from complex interactions of unconscious matter and fields”. Instead, panpsychists believe that there's consciousness (or there are phenomenal properties) all the way down to the particle and all the way up to the animal brain. Thus there's no need for (radical) emergence.
Idealism and Anti-Realism
On the surface at least, Hoffman seems to take a very strong idealist position when he says that “brains and neurons do not exist unperceived”. (This is exactly what Bishop Berkeley argued; thought not, of course, about “brains and neurons”.) Now this isn't an expression of anti-realism because an anti-realist wouldn't say that any x doesn't exist “when unperceived”. He'd simply say that our perceptions “colour” what it is we take to exist. And there's no way around that.
All this displays the very common problem of conflating (or confusing) idealism and anti-realism.
Despite having just stated that, there is a strong sense in which one can derive idealist conclusions from anti-realist statements. That is:
i) If we describe things as “brains" and "neurons”,
iia) and those descriptions are contingent - and dependent – upon persons/observers, concepts, theories, etc.,
iii) then perhaps we may as well conclude that brains and neurons “do not exist unperceived”.
That is, brains and neurons (as well as other objects) don't exist until we describe/observe them. (This echos, to some extent at least, the debate which surrounded Niels Bohr's Copenhagen interpretation of quantum mechanics – see later section.) That's true enough. However, why embrace the idealist conclusion that everything that exists only does so in the minds of persons? That route leads to idealism, subjectivism, solipsism and woo.
In addition, what does Hoffman mean when he states that brains and neurons “have no causal power”? I ask that question because he doesn't explain it in the passages just quoted (though he may well do elsewhere). What's more, he concludes that this lack of causal power is “why we've never been able to boot up consciousness from neural activity”. So what does all that mean?
Kant's Transcendental Idealism
Hoffman's main problem with Immanuel Kant's position on noumena is that he believes that it's not scientific. Or, less strongly, he believes that Kant's position doesn't look promising from a scientific perspective.
As Hoffman puts it about one “interpretation” of Kant:
“This interpretation of Kant precludes any science of the noumenal, for if we cannot describe the noumenal then we cannot build scientific theories of it.”
Yet Hoffman's own conscious realism isn't a scientific theory either. (Sure, it's clearly the case that Hoffman believes that it is.) He then says that
“[c]onscious realism, by contrast, offers a scientific theory of the noumenal, viz., a mathematical formulation of conscious agents and their dynamical interactions”.
Hoffman often defends his conscious realism by talking about its “mathematical models”, etc (or by using the words above – i.e., “a mathematical formulation”). Despite that, only the mathematical models or “formulations” used in conscious realism are scientific (or mathematical). All the additions to that are examples of speculative philosophy. So this isn't that unlike people using mathematics and scientific terminology to defend - or back up - astrology, astral travelling, ley lines, Creationism, etc. (This aspect of Hoffman's conscious realism can't be tackled now. I've tackled it here.)
In addition, if conscious realism really “offers a scientific theory of the noumenal”, then it's not the noumenal that it's offering a scientific theory of. Of course this may be terminological pedantary in that, to Hoffman, the noumenal isn't in fact noumenal at all. Thus he believes that he can offer a scientific theory of it. Kant, on the other hand, created a theory in which noumena were – by definition – not only beyond science, but also beyond Hoffman's cognitive agents.
Hoffman then expresses a position that isn't at odds with either anti-realism or Kant's transcendental idealism. He writes:
“Many interpretations of Kant have him claiming that the sun and planets, tables and chairs, are not mind-independent, but depend for their existence on our perception. With this claim of Kant, conscious realism and MUI theory agree. Of course many current theorists disagree.”
The wording in the above isn't quite right. Hoffman says that Kant believed that
“the sun and planets, tables and chairs, are not mind-independent, but depend for their existence on our perception”.
Surely it's best to say that some things (whatever they are) exist mind-independently. The problem is that they don't exist as the sun, planets, tables and chairs. That is, the fact that we see these things this way is a result of our contingent modes of “perception”; as well as our concepts, theories, languages, etc. However, this is still not idealism because Kant's noumena exist. In addition, they aren't the contents of consciousness. So this is transcendental idealism; not immaterialism or subjective idealism.
To sum up. Whatever is “behind” (or the cause of) our perceptions is not itself dependent on consciousness (or on our perceptions).
The Copenhagen Interpretation
Hoffman states the following:
“Scientists believe that space, time, and objects exist even if they're not perceived. That's a fundamental assumption of most.”
So let's reiterate what's just been said above (i.e., before the subheading). Scientists (or at least some/most of them) do believe that objects exist even when not perceived. However, when they are perceived, then they're given (as it were) a determinate form – a form which is down to our contingent theories, experiments, perceptions/observations, concepts, languages, etc.
Secondly, not all - or even most - scientists “believe that space, time, and objects exist even if they're not perceived”. There have been (for many years) many physicists working on the non-existence of both space and time, for example. (Admittedly, that's a question of the very existence of space and time and it has little to do with our perceptions.) In addition, scientists aren't philosophers. Thus most scientists have little time for phrases like “objects exist even if they're not perceived”.
This leads us to the Copenhagen interpretation of quantum mechanics.
Hoffman often applies the Copenhagen interpretation to the “classical” (or macro) scale. (Indeed Hoffman himself mentions the Copenhagen interpretation on a few occasions and at one points says that "most proponents of the Copenhagen interpretation embrace it only for the microscopic realm".) For example, here's Hoffman applying it to DNA:
“For instance, [conscious realism] entails that DNA does not exist when it is not perceived. Something exists when we don’t look that causes us, when we do look, to perceive DNA, but, whatever that something is, it’s not DNA.”
Perhaps this is a bad example because at least DNA is a microphenomenon, if not a subatomic phenomenon. (Though DNA is determined by – and dependent upon - quantum phenomena.) Elsewhere, however, Hoffman applies exactly the same argument to brains (as a whole), cups, trees, and other everyday macro-objects. Now, to state the obvious, there's a vast difference between a electron (for example) and a tree (for example).
Another point is that Niels Bohr didn't embrace idealism. To put it simply. There's also a big difference between the stress on how we gain access to (as it were) reality and the idealist position that it's all about what goes on in one's head. (Or within what Hoffman deems to be a Collective Head.) Anti-realists accept that there is a mind-independent world. However, human beings only gain access to that world through their brains, consciousnesses, concepts, languages, etc. Idealism, on the other hand, seems to have it that literally everything is in the minds of subjects (or agents). And, if that's correct, then that puts idealism and anti-realism in radically different places. Yet, as is the case on so many occasions, anti-realism is basically seen as idealism (or, at the least, as a variety of idealism). Having said that, what Hoffman himself argues doesn't make this distinction clear. And, because of that, it can be argued that Hoffman's position is idealist rather than anti-realist.