Modern Philosophy is mired in a confusion of terms. However, the terms themselves are not central to a discussion of metaphysics - the various philosophical positions they represent are. My task here is to throw light on these positions by demarcating the boundaries between these positions and what they commit us to for coherence and consistency. I would use the symbol $ for saying ‘I hope I am justified in using these terms interchangeably in this context’, and I would be grateful for the reader to point out when I am not.
Realism, Anti-Realism, Idealism, Materialism and Dualism are metaphysical theories which attempt to account for the world as it appears to us, and distinguish the appearance, if possible, from reality. The Realism - Anti-realism dichotomy partitions the metaphysical spectrum into two mutually exclusive, collectively exhaustive parts ; with Idealism, Materialism and Dualism being specific subsets which lie under one or the other category.
Realism and Anti-realism differ in their conceptions of what the objects which appear to us represent. For realism, the objects that we perceive through our sense - by sight, sound, smell, touch or taste, are objects which exist in the real world. Their existence and properties exist independent of any human contact. (Once a mind-independent reality is assumed, the question as to how we interact with it can further divide realism into direct and indirect realism: the former posits the view that reality is as we perceive it, while the latter that we only perceive an indirect representation of reality.) Realism does not deny the existence of abstract mental constructs - it possibly couldn’t: it would be absurd, if not incoherent, to say that our thoughts and feelings need not exist, for if they don’t, then what does? Thus, it either accounts for mental content as a phenomenon having its own existence separate from the existence of matter in the real world (dualism), or as a manifestation of physical states of our brain (materialism or physicalism ($)).
Thus, both Dualism and Materialism fall under the ambit of realism as they posit the existence of reality independent of the mind. Materialism (or physicalism ($) posits that everything in the world is composed of matter. By this view, then, what we perceive to be purely abstract mental constructs - our thoughts and feelings and ideas and experiences - are equivalent to certain neuro-physiological states of our brain. Dualism, however, posits the existence of purely mental phenomenon different from physiological phenomenon.
Anti-realists, on the other hand, deny the objects of our sense-data any status other than that of a sense-data. Objective (or external, or mind-indepedent ($)) reality for anti-realists, then, either does not exist (idealism, or phenomenalism ($)?) or is something we can never know of. The latter view is susceptible to be confused by indirect realism. However, indirect realists maintain that we can know at least something of reality by indirect representation, while for anti-realists nothing can be known.
Idealism, then, is a specific form of anti-realism, which asserts that reality is mentally constructed. Idealism derives its name from its position that ideas are everything there is, and the only things. When I perceive a red rose, I do not (and cannot) refer to at an actual red rose which exists ‘out there’ independent of my observation, but only to the properties of redness, rose-like odour, rose-like tactical perception existing solely in my mind. Moreover, the combinations of these properties which exist in my mind is what it is for a red rose to exist, and nothing else. ”To be is to be perceived”.
Thus, on our spectrum of metaphysical positions, if Idealism is a radical form of anti-realism, Materialism a radical form of realism, and Dualism stands at the moderate middle, positing that mental and physical are separate and different phenomenon. (It is possible to imagine a different scale, partitioned by Dualism and Monism and Pluralism, where both Idealism and Materialism fall under the category of monist theories standing in contrast to dualist ones. However such a categorisation is a very general, not specific to metaphysical enquiries, where the categorisation outlined above is more germane).
An important question which we run into when discussing theories of a mind-indepedent reality is what it means for an object to exist when not being perceived or if human beings ceased to exist. This can be articulated as ‘“If a tree exists in a forest and no one is around to perceive it, does it really exist?” This question is often treated as a rhetoric against anti-realism, because nothing in our experience suggests that a tree ceases to exist. If it is perceived now and not perceived in the future, it simply doesn’t disappear. We can, to a high degree of reliability, predict that when we go back to the forest, we will again perceive the tree. If anti-realism is true, then why is it that we can make such reliable predictions about the real world based on our sense-data? To make the question more general, consider this: why is it that whenever we have a visual sensation of a red rose, we have the same tactical or olfactory senation as well? (Why can’t we perceive the redness of a rose and the smell of a rose separately, under different circumstances?) Why is it that when Robinson Crusoe sees a footprint in a sand, he can assume that there is a man around? Why is it that when I perceive all the properties of a red rose bundled together (which happens overtime one of the properties is experiences, as earlier noted), other people also experience the same properties? What generate such patterns, coherence and consistency in our mental content, almost as if they were true independent of our minds?
While any realist theory can easily answer these questions by an appeal to reality independent of our minds, anti-realists have a challenge at hand, and they respond to it in different ways. Most versions of anti-realism, Berkeley’s idealism for example, attribute this high coherence of our ideas and patterns in reality to a Supreme Mind (or God($), and thus have to commit to theism, which I believe to be a stronger thesis than idealism itself. (As another example, Putnam’s internal realism would attribute the patterns and coherence to the structure of our mind, which could be causally dependent on an external, unknowable reality. Note that Putnam’s internal realism, though a realist doctrine in the sense that there exists a mind independent reality ‘out there’, is an anti-realist doctrine according to the categorisation described above, since antirealism as defined here includes possibility of external but unknowable reality). However, idealists will not maintain that positing the existence of a Supreme Mind carries any more of a metaphysical burden than positing the existence of a mind-independent reality does, because the existence of mind-dependent objects (thoughts and feelings) are the only things whose existence we can be certain of, and since the Supreme Mind is just a mind like ours, its existence is the simplest assumption one can make.
The second most prominent question that any theory of mind-independent reality must tackle is the Brain-in-a-Vat problem, which derives its substance from the existence of hallucinations and illusions. The best demonstration of the Brain-in-a-Vat though experiment to a modern audience is in the movie The Matrix, where human beings live in an artificial reality called the matrix which is programmed by the machines to resemble just like what our world looks like. Thus, while the earlier challenge weighed down on anti-realists; this second question weighs down on realists : How does a realist know that we are actually not living in a Brain-in-a vat, or equivalently, a simulated reality?
For the idealist anti-realists, this does not cause a problem, since according to them we are living in a simulated reality, a simulation created by the Supreme Mind; there being nothing else. For the rest of the anti-realists, we are living as a brain-in-a-vat, with what lies outside the vat unknowable to us.
Realist can respond to the brain-in-a-vat in different ways, but it depends on the formulation of the problem. For example, if presented the traditional brain-in-a-vat problem has an implicit support for the materialist, since it precludes the fact that mental content can also be simulated by purely brain-based physical phenomenon.
30 January 2015