I understand 'antirealism' to mean that it useless to talk about the term 'reality' except in cases where consensenus is being sought as to 'what is the case'. Scientific paradigms are examples of where that consensus operates regarding successful prediction and control of events, and it is 'experienced events' which replace 'physical reality' for the antirealist. The traditional dichotomies like subjective/objective or mental/physical are misleading in understanding 'antirealism' because they are predicated on lay concepts of an observer independent reality. Such dichotomies are considered futile by philosophical pragmatists.

I understand there can be different versions of antirealism such as epistemic (knowledge) and semantic ("meaning of statements"). I was referring to metaphysical antirealism which is the idea that "nothing exists outside the mind". I was wondering what the scientific implications would be of such a viewpoint.

I was referring to metaphysical antirealism which is the idea that "nothing exists outside the mind". I was wondering what the scientific implications would be of such a viewpoint. — Michael McMahon

Wouldn't the mind remain objectively real?

"Even if I happen to be a brain in a vat at this moment—all my memories are false; all my perceptions are of a world that does not exist—the fact that I am having an experience is indisputable (to me, at least). This is all that is required for me (or any other conscious being) to fully establish the reality of consciousness. Consciousness is the one thing in this universe that cannot be an illusion."
- Sam Harris

Well, if consciousness cannot be an illusion, all that stems from it would be equally genuine.

The mind is still mysterious. It gets deceived while dreaming but then dreams are also mysterious. The external world can only be inferred from one's perception of it.

It gets deceived while dreaming — Michael McMahon

How so?

An antirealist is "a person who denies the existence of an objective reality". It sees "no access to a mind-independent reality, even if it exists". But "if you don't believe in scientific
realism, you can still do and use science. You can believe that science may not tell us about a physical world but rather tell us about a mental one instead". — Michael McMahon

These quotes and your interpretation of them are all made from an implicitly realist point of view, and furthermore, one which sees ‘mind’ and ‘matter’ or ‘subjective’ and ‘objective’ as totally seperate domains (as Fresco notes). So in this understanding, ‘reality’ is either ‘objective’, really there, given; or it’s ‘subjective’, ‘in the mind’.

But I don’t think the issue is nearly so clear cut as that. What I think the realist view forgets, ignores or excludes is the role of judgement in anything we see or know about the world. After all there is no light inside the skull. When we see something, the process of seeing relies on the interpretation of visual sensations - even apparently simple knowledge acts are interpretive. And I think a credible ant-realist epistemology simply acknowledges the fundamental role that the mind plays in any knowledge act, whether of objects or anything else.

"When I look at the sky, the sky I see is inside my head. This means that my skull must be beyond the sky!"
- Lehar

Superdeterminism: "not only is our behaviour determined, but it is determined precisely in such a way as to prevent us from seeing that the world is deterministic".

So are you saying our own thoughts and judgements are not real; perhaps they are deterministic and not truly our own? That brings up the problem of free will. Perhaps the different issues in consciousness are related. Must an antirealist also be a determinist? It's a big topic.

It's a big topic. — Michael McMahon

That's for sure. Have a read of this.

by metaphysical antirealism, do you mean idealism? One such popular proponent, at least in early modern era, was of course Berkeley. But Berkeley's idealism is a bit different (as far as I can tell) from modern conceptions of antirealism, many of which are presupposed from constructionist perspectives...antirealism can refer to anything from skepticism (in epistemology) to better understanding the role language/society has on our conceptions of reality (intersubjectivity)...

I used to consider myself an antirealist, largely because I was led to it through the constructivist conception of reality-I still enjoy various tenets in antirealist thought, especially with regards to the problem of consciousness. New Mysterianism (or anti-constructive naturalism/cognitive closure) can be reconciled with antirealism, that is, it holds that certain knowledge is outside the domain of human understanding (if it exists at all), at least for now.
I've always seen metaphysics with a very definitive line between the two, that is, the "realist" and "antirealist" camp, and within these two dichotomies, one can (usually) reconcile various theories within and overlapping other areas of philosophy (this is a very over-simplified explanation, all of these concepts become increasingly complex in their own right)

realist: materialism, physicalism, reductionism, eliminativism ect.
antirealist: idealism, transcendentalism, subjectivism, noumenon?, constructivism, skepticism, post-modernism, qualia,

I'm currently putting forward an argument along these lines, that while an 'objective' and absolute account of reality may exist, us as human beings, do not have the capacities to appreciate or otherwise understand and comprehend such a reality-as we are forever entangled within our subjective realities (as @Wayfarer has noted)...for more on this, start with Nagel
I presume, that other beings, insofar as they experience subjective reality (I argue also that most, if not all, living things experience some form of subjective reality) cannot escape their subjective realities either, and while humans have made valiant attempts at categorizing, and otherwise understanding the (what appears to be at least) physical world, these attempts are incomplete, and in some cases grossly incorrect, laden with human biases and undetected human limitations.

To answer your original question, science is threatened. There is a large break between science and philosophy that occurred in the last century or so...hence why philosophy is largely relegated to the page of uselessness, while science is upheld as the new faith, new religion (scientism). Nagel mentions this too. Science reassures us of our human superiority, safety, and ability, it plays on the man vs. nature trend, and in recent times, is famed as being what will "save us" from ecological collapse. These are major issues within the theoretical understanding of science as a field, that I hope in the next decade or so will come under scrutiny.

And I think a credible ant-realist epistemology simply acknowledges the fundamental role that the mind plays in any knowledge act, whether of objects or anything else. — Wayfarer

That doesn't sound right because it references the objective, which is to suggest an external reality that the anti-realist can't commit to. What you described seems like indirect realism.

"Indirect realism is broadly equivalent to the accepted view of perception in natural science that states that we do not and cannot perceive the external world as it really is but know only our ideas and interpretations of the way the world is." https://en.wikipedia.org/wiki/Direct_and_indirect_realism

"When I look at the sky, the sky I see is inside my head. This means that my skull must be beyond the sky!"
- Lehar — Michael McMahon

Or your skull is below the sky, and notes the sky through the imprint the sky leaves upon it - though it cannot directly note the sky.
Of course going back to the original query, that begs the question, how does what shouldn't be there leave an imprint? And a different question: are you incapable of directly seeing the sky, even if you haven't done so yet?

Superdeterminism: "not only is our behaviour determined, but it is determined precisely in such a way as to prevent us from seeing that the world is deterministic". — Michael McMahon

Look at a multiple choice test.
All the answers are predetermined, but you're free to pick whichever one you like.
There's choice in chance and chance in choice. You're free to make of it what you will.

Going back to:

An antirealist is "a person who denies the existence of an objective reality". — Michael McMahon

That would be self-denial.
An anti-realist would have to deny his anti-realism to comply with it.
Any imposition against reality is inescapably objective by itself, and likewise subjective when viewed as a part.

An antirealist is "a person who denies the existence of an objective reality" — Michael McMahon

That's the thin version. There's a bit more to it than that. It's more about the meaning of propositions than about the reality of the objects around us.

A realist might say that "Here is a cat" will be true exactly if there is a cat, here. The cat is independent of the utterance, and will be there whether the utterance is made or not, and indeed independently of the meaning of the utterance.

An antirealist might rather say that the truth of "Here is a cat" depends at least to some extent on the circumstances in which the utterance takes place, especially the way the utterance is used to 'carve up' the world; so to some extent for the antirealist there is only a cat if we all decide that's how we will talk...

Anti-realism might be a useful device for philosophical sceptism or to counter the most egregious overreaches or oversimplifications that people do in the name of realism. As a general World-view it might not be the most useful things.

Physical reality is 3-dimensional. So would anti-realism imply that the mind is 2-dimensional due to the seeming non-existence of the physical world? — Michael McMahon

Given what I said above, I hope it is clear that there is little difference between realists and antirealists in what they assert about the way things are. Both will say that there is a cat.

Nor need an antirealist deny that there is a physical world. It is open to them to say that if we talk as if there is a physical world, then by that very fact there is indeed a physical world.

Lastly, even if reality was solely mental, I think the world would still be real in the sense that other people exist to perceive it. Even if it isn't physical in nature, it would have to be some sort of projection that we're all participants in. — Michael McMahon

And this is I think a very salient point; for how can one explain the astonishing degree of agreement between you and I and Aunty Millie and Fred over there, if there is no 'reality' that is somehow shared by us all?

Two possibilities occur to me, neither of them very palatable. Perhaps me and Aunty Millie and Fred over there are your creations, you being all that there is. Or perhaps you and me and Auntie Millie and Fred over there all partake in some 'overmind' that sets us up to think much the same thing. Solipsism or panpsychism.

Good post ! If you are following my 'Existence is relative' thread, you may find we have some common ground.

Ive looked over your thread, its a bit waylaid by opposing opinions but I think I understand and appreciate what you are getting at. :)

https://en.wikipedia.org/wiki/Illusory_motion

I've been thinking a bit about dualism. If the mind is fundamentally and ontologically separate from the body, then how does relative motion occur between the mind and the physical world? If someone walks forward 10 meters in space, doesn't their sentient mind also move forward precisely 10 meters with their body? But in order for this corresponding relative motion to occur the mind would necessarily have to be part of the physical world. Only material objects can move relative to each other. Unless the locus of consciousness were somehow forever stationary; that the brain just relays signals to a static and unmoving mind. This would imply that the motion of the mind is illusory and that only the body moves. The mind would solely move through the dimension of time.

I do not see why "physical reality" being three dimensional means that "physical reality" has a monopoly on three dimensional realities.

I feel no obligation to accept your definition of anti-realist. I am unaware that there is any consensus on a definition of an anti-realist.

I question whether our (human) modes of access to being necessarily exhaust all modes of access to being.

I would be surprised if they did.

There's a lot of debate about chaos theory and free will; that chaos is still deterministic even if it's unpredictable. But obviously over larger time-scales it becomes even more unpredictable.

Likewise short-term behaviour (like whether I choose to lift my hand or not) might be completely deterministic. But perhaps there's scope for free will to act in a more gradual way that affects long-term memory and personality.

Scepticism can lead to very existential living. Doubt isn't bad like Christians think. I believe you guys exist ontically, but I have to know someone well to not be somewhat solipsistic towards them. It's fun to doubt someone exists and then to discover their room and bed

I was referring to metaphysical antirealism which is the idea that "nothing exists outside the mind" — Michael McMahon

That's radical idealism...

We're all subject to different spaces, but an invention of man makes us all believe (falsely) we're subject to the same time. I've thought the invention of the mechanical clock true evil before, and stand by it. In other words, objective reality wouldn't exist without this subversion of the truth of separate times for separate individuals.

I was referring to metaphysical antirealism which is the idea that "nothing exists outside the mind". — Michael McMahon

Since this topic was resurrected, I want to point out the contradiction of antirealism, defined in the OP as "denial of the existence of an objective reality" and the statement quoted here of "nothing exists except X" where X is the mind in this case. Those two definitions are mutually exclusive, the latter being a form of realism typically knows as idealism, which posits the reality of experiences.

I personally have found 'existence of an objective reality' to be a meaningless concept, and hence see no reason to assert it, which is a little different than actively denying it, so I'm not sure if I qualify as an antirealist.

I understand 'antirealism' to mean that it useless to talk about the term 'reality' except in cases where consensenus is being sought as to 'what is the case'. Scientific paradigms are examples of where that consensus operates regarding successful prediction and control of events, and it is 'experienced events' which replace 'physical reality' for the antirealist. The traditional dichotomies like subjective/objective or mental/physical are misleading in understanding 'antirealism' because they are predicated on lay concepts of an observer independent reality. Such dichotomies are considered futile by philosophical pragmatists. — fresco

In other words, anti-realism logically leads to solipsism. Where is this consensus taking place if not in the real world with real human beings? "Consensus" is a term lacking any meaning for an anti-realist.

Nor need an antirealist deny that there is a physical world. It is open to them to say that if we talk as if there is a physical world, then by that very fact there is indeed a physical world. — Banno

What does "talking" mean if there isnt a medium that carries this information (that there is something called a physical world that contains cats) between minds?

I personally have found 'existence of an objective reality' to be a meaningless concept, and hence see no reason to assert it, which is a little different than actively denying it, so I'm not sure if I qualify as an antirealist. — noAxioms

What would the phrases, "living under a rock", or "living in a bubble" mean for an anti-realist?

Are there other minds, or other bodies? Why do we perceive other minds as other bodies?