02 June 2016

Take off the kid gloves: dualism is a pseudoscience

We non-believers are pretty good about calling out religious people who subscribe to young-Earth creationism or 'intelligent design'. They're pseudosciences — bolstered with arguments often couched in scientific-sounding language, but ultimately not just unsupported by data but in stark, irreconcilable conflict with the data we do have.

For some reason, most of us are a lot easier on dualists — those who insist the mind is somehow independent of the brain. Granted, there's always neuroscientist and skeptic Steve Novella, who definitely doesn't pull any punches, but a firm condemnation of dualism just isn't quite as prevalent in the public community of skeptics and non-believers as arguments against evolution deniers.

Maybe it's because the mind sciences — neurobiology, neurocomputation, and cognitive science — are a bit more esoteric. They're characterized by a somewhat obscure lexicon that doesn't always lend itself to concisely packaged arguments. But that should not obscure the fact that from a scientific standpoint, there is no dispute that the mind is wholly caused by the brain. You are not going to comb through an issue of Scientific American Mind and find the latest research from dualists because, well, dualists aren't actually doing any research. That's because unlike a brain-emergent theory of mind, dualist theories of mind don't make predictions and accordingly are unfalsifiable. Instead, they live in the margins as post hoc rationalizations for data produced by the hard sciences of the mind.

Dualism is conceptually ambiguous

A common refrain from dualists is that since the mind is not material, it cannot be studied empirically. Science, they say, studies the 'natural world'. This allows dualists to have their cake and eat it, too: they can try to explain scientific data in the context of dualism without ever producing a working scientific theory that would actually generated testable hypotheses.

But this rationalization fails at a basic conceptual level.  Sean Carroll concisely summarizes the problem in an op-ed for Scientific American:
Claims that some form of consciousness persists after our bodies die and decay into their constituent atoms face one huge, insuperable obstacle: the laws of physics underlying everyday life are completely understood, and there's no way within those laws to allow for the information stored in our brains to persist after we die. If you claim that some form of soul persists beyond death, what particles is that soul made of? What forces are holding it together? How does it interact with ordinary matter?
And Sam Harris, in a discussion with the late Christopher Hitchens, David Wolpe, and Bradley Artson Shavit, summarized the issue on similar terms:
Science is not in principle committed to the idea that there’s no afterlife or that the mind is identical to the brain.
If it’s true that consciousness is being run like software on the brain and can – by virtue of ectoplasm or something else we don’t understand – be dissociated from the brain at death, that would be part of our growing scientific understanding of the world if we discover it.
But there are very good reasons to think it’s not true. We know this from 150 years of neurology where you damage areas of the brain, and faculties are lost. You can cease to recognize faces, you can cease to know the names of animals but you still know the names of tools.
What we’re being asked to consider is that you damage one part of the brain, and something about the mind and subjectivity is lost, you damage another and yet more is lost, [but] you damage the whole thing at death, we can rise off the brain with all our faculties intact, recognizing grandma and speaking English!

All of these discussions point to two fundamental conceptual problems with mind-body dualism:

  • Dualists do not have a theory of what the mind is, or even an unambiguous description of a non-material substance
  • More importantly, dualists do not have a testable hypothesis that would explain how the immaterial mind causally interacts with the physical brain — or even why it should in the first place.  

The evidence is overwhelmingly on the side of a material account of the mind

Aside from the lack of empirical evidence or even a coherent theoretical structure from dualists, there are many reasons to be confident that the mind is caused by the brain. 

Embodied cognition

Evidence from cognitive linguistics shows that basic conceptual systems used for reasoning are defined not just by our brains, but by our motor systems. Gestalt perception and motor schemas share neural circuitry with higher-level abstraction. From Lakoff:
• Our brains are structured so as to project activation patterns from sensorimotor areas to higher cortical areas. These constitute what we have called primary metaphors. Projections of this kind allow us to conceptualize abstract concepts on the basis of inferential patterns used in sensorimotor processes that are directly tied to the body. [Philosophy in the Flesh, Kindle location 962]
Primary metaphors are such concepts as big is important (tomorrow is the big day!), love is closeness (the stress of their jobs drove the couple apart), more is up (stock prices skyrocketed!), bad is smelly (this movie stinks), etc. There are a great deal of these metaphors, and they are integral to our process of reasoning — we literally cannot reason without them.

Moreover, these metaphors have a neural grounding in what is called conflation. Lakoff, again:
In research on metaphor acquisition in children, Johnson (Al, 1997b, c) studied the Shem corpus in detail. This is a well-known collection of the utterances of a child named Shem, recorded over the course of his language development (D, MacWhinney 1995). In an attempt to discover the age at which Shem acquired a commonplace metaphor, Johnson looked at Shem's use of the verb see. His objective was to discover the mechanism involved in the acquisition of metaphor. He had hypothesized conflation as a possible mechanism, and he wanted to find out whether there is indeed a stage of conflation prior to the use of the metaphor. His test case was Knowing Is Seeing, as in sentences like "I see what you're saying." In such metaphorical examples, knowing is the subject matter. Seeing is the metaphorical source domain used to conceptualize knowledge, but it is not used literally.
Johnson discovered that, prior to using metaphor, Shem went through a stage in which the knowing and seeing domains were conflated. Since we normally get most of our knowledge from seeing, a conflation of these domains would have been expected. In such conflations, the domains of knowing and seeing are coactive and the grammar of know is used with the verb see in a context in which seeing and knowing occur together-for instance, "Let's see what's in the box." Here, seeing what's in the box correlates with knowing what's in the box. [Philosophy in the Flesh, Kindle location 633]
The case for embodied cognition is vastly more complex than these few snippets can illustrate, but what's important to take from this is that the embodied account only makes sense in the framework of a physical account of the mind, and it makes direct, falsifiable predictions about the structure of our conceptual systems from the neural circuitry of our brains.

Moreover, if dualism were true, there would simply be no need to describe conceptual systems in the terms of our embodiment and our neural circuitry. As always the dualist position can be shoehorned in as part of a weaselly post-hoc rationalization of data, but dualism does not produce a theory of mind that predicts or necessitates embodied cognition — cognitive linguistics, however, does precisely that.

Science predicts a relationship between cognitive states and brain states

Another famous argument of dualists is that the relationship between brain states and cognitive states is strictly correlative, not causal. But aside from suffering from the same deficiency of being only a post-hoc rationalization of data, a scientific account of the mind predicts states of cognition as outcomes of brain states. These predictions are falsifiable, reliable, and reproducible. Steve Novella elaborates:
As we have learned more and more about brain function, we have identified many modules and circuits in the brain that participate in specific functions. During the Afterlife debate I gave a few of my favorite examples.
Disruption of one circuit, for example, can make someone feel as if their loved-ones are imposters, because they do not evoke the usual emotions they should feel.
Disruption of another circuit can make a person feel as if they are not in control of a part of their body – so-called alien hand syndrome.
A stroke that leaves the ownership module intact but unconnected to the paralyzed limb can rarely result in a supernumerary phantom limb – the subjective experience of having an extra limb that you can feel and controlled (but that does not exist).
Seizures are also a profound area of evidence for the mind as brain theory. Synchronous electrical activity in particular parts of the brain can make people twitch and convulse, but also experience smells, sounds, images, feelings, a sense of unreality, a sense of being connected to the universe, an inability to speak, the experience of a particular piece of music, a sense of deja vu, or pretty much anything you can imagine. The subjective experience depends on the part of the brain where the seizure occurs.
There is also copious evidence from strokes and other forms of brain damage. As a practicing neurologist I can examine a patient with a stroke and with a high degree of accuracy predict exactly where the lesion will be in the brain on subsequent imaging. Everything you think, do, and feel has a neuroanatomical correlate in the brain, and if that function is altered or not working, that will predict where the lesion can be found.
Not only does dualism fail to account for such correlates with any sort of theoretical framework, but there's no reason to think these predictions should hold on a dualistic account. A material account of the mind requires such predictions to be reliable and valid, as they are. Dualism is ambiguously and equivocally defined, so it's not entirely clear what a dualistic theoretical framework would require. But since no dualistic 'theory' makes testable predictions, there's no reason to think dualism would require any particular neurocognitive predictions to hold.

Worst of all for dualism is perhaps the most obvious problem: cognitive states have never been observed to occur without brain states. We cannot communicate with dead people. When someone has suffered severe brain damage — via a stroke, accident, or some other misfortune — specific and often counter-intuitive changes to personality, memory, awareness, empathy, or communication may be adversely affected. Not only has a neurocognitive model of the mind been able to successfully predict these cognitive states, but they've been able to show with great detail the biological mechanisms at play.

The last bastion for dualism lies not in science, but in classical philosophy. As the theologian Edward Feser claims, "The mind knows itself directly, without the mediation of a mental image or any other representation." Cognitive science has shown this claim to be unequivocally false. You have absolutely no knowledge of or choice in the formation of the metaphors that form the structure of your reasoning — and the embodied, metaphorical structure of reasoning could not have been predicted by philosophers. Lakoff, again:
[There] is no Cartesian dualistic person, with a mind separate from and independent of the body, sharing exactly the same disembodied transcendent reason with everyone else, and capable of knowing everything about his or her mind simply by self-reflection. Rather, the mind is inherently embodied, reason is shaped by the body, and since most thought is unconscious, the mind cannot be known simply by self-reflection. Empirical study is necessary. [Philosophy in the Flesh, Kindle location 80]
A neurocognitive account of the mind is robustly supported by scientific data that spans multiple interrelated disciplines. It's comprised of sound theoretical models that have successfully and reliably made falsifiable predictions. Dualism trudges on, clinging desperately to the coattails of scientific progress with post hoc rationalizations of scientific data, most likely spurred by fear of facing the entailments of a successful scientific theory of mind: souls probably do not exist, and when you're dead you're gone forever. But as Carl Sagan famously said, "It is far better to grasp the universe as it really is than to persist in delusion, however satisfying and reassuring". Let's stop treating dualism as anything other than the nonsense that it is — an antiquated folk theory of mind that belongs in the dustbin along with young-Earth creationism and intelligent design.

29 May 2016

Lakoff: Math is made up by your brain

Tonight I was on YouTube, and in my 'recommended videos' section there was a selection from the channel Closer to Truth asking physicist Max Tegmark the old granddaddy of questions, "Why is there something rather than nothing?" Tegmark goes on to expound on his view that the universe is fundamentally mathematical and that mathematics are discovered, not invented.

Tegmark's view is an example of a view called mathematical Platonism, a form of mathematical realism which holds that:
  • There are mathematical objects
  • Mathematical objects are abstract
  • Mathematical objects are independent of intelligent agents and their language, thought, and practices.
There are several difficulties that this point of view faces, both conceptually (what, exactly, is an "abstract object" and how does it causally interact with the brain?) and given what we actually observe here in the physical universe. Alexander Vilenkin touched on Tegmark's ideas in his book Many Worlds In One:
The number of mathematical structures increases with increasing complexity, suggesting that “typical” structures should be horrendously large and cumbersome. This seems to be in conflict with the simplicity and beauty of the theories describing our world.
It just so happens that in the 'related videos' sidebar, YouTube recommended this vid from George Lakoff on embodied mathematical cognition — a condensed version of his book Where Mathematics Comes From. It's a scientific alternative to folk theories of mathematics like mathematical Platonism and though it's a relatively nascent field with plenty of challenges ahead, there's growing evidence that it's correct [1, 2, 3]. It's not without controversy, but challenging intelligent people to case aside philosophies entrenched in academia for centuries is inevitably going to meet resistance.

My take is that the conceptual ambiguities intrinsic to mathematical realism put it at a disadvantage to embodied mathematical cognition, which builds on research from the broader field of embodied cognition. Is it true? I don't know. And as a non-mathematician, some of this stuff is over my head. But I think it's fascinating as hell, and the fact that it grounds conceptual abstraction within the purview of scientific inquiry instead of mysterious 'metaphysical realms' is a big reason why I'm such a fan of Lakoff's work.

Anyway... here's the lecture. 

20 May 2016

The Oklahoma State Legislature makes me embarrassed to live in the state

Just this week, the legislature in my state of Oklahoma has:

And just a couple of months ago, the passed legislation that would ask voters to restore the 10 Commandments monument to the Capitol after the state supreme court ruled it unconstitutional.

Now look, this is bad enough. Most of this legislation is flagrantly unconstitutional. Our governor Mary Fallin, by most accounts an incompetent stooge, at least had the foresight to veto the abortion law and save the state hundreds of thousands in legal fees from a sure-loss court case. 

But here's what really grinds my gears: shit is bad in Oklahoma, and a good deal of it is the legislature's fault. Years of Laffer-Curve economics has led the state to a record budget shortfall that is threatening funding for medicaid, teachers, schools, public attorneys, and much much more. And Oklahoma is just one of many GOP-led states whose Laffer-Curve policies have led to steep red ink.

You'd think this would lead to a little introspection among the legislature: Golly, maybe supply-side economics aren't working! Pfff. Of course not. Tax cuts have become such a central part of the GOP milieu that it's unfathomable that a candidate would campaign without them. Conservatives love to chide Bernie Sanders supporters for wanting "free stuff", while presumptive GOP nominee Donald Trump offers a tax-cut plan that would cost nearly $10 trillion over the next decade, with most of the cost coming from cuts to top earners. But hey, I guess that's just "free stuff", right? 


Teachers are losing their jobs. Schools are facing closings, 4-day weeks, larger class sizes, and reduced bus routes because of massive shortfalls in education funding. Public attorneys aren't getting funding. The House passed a bill cutting 111,000 people from medicaid

At a time when the state legislature should be hard at work on solutions to these problems, they're passing frivolous laws and pandering to the most extreme of their constituency. Unsurprisingly, the non-profit Center for Public Integrity and Global Integrity gave Oklahoma an "F", citing a lack of transparency, corruption, inequality, and access to public information. The one bright spot is in the state's auditing office, which independently found "fraud and waste across a broad spectrum of public bodies".

It's not entirely clear what can be done in the short term. I just hope that the widespread knowledge of the legislature's incompetency inspires more urban young people to get out the vote.

Robert Epstein: Your brain is not a computer

For decades, the neurocomputational metaphor has been an integral part of research that attempts to bridge the gap between the biological structure of the brain and cognition. But it is, alas, only a metaphor. In an essay for Aeon, psychologist Robert Epstein argues that your brain does not process information, store knowledge, or retrieve memories. In short: it is not a computer.

Some choice quotes:
We don’t store words or the rules that tell us how to manipulate them. We don’t create representations of visual stimuli, store them in a short-term memory buffer, and then transfer the representation into a long-term memory device. We don’t retrieve information or images or words from memory registers. Computers do all of these things, but organisms do not.
[The] IP metaphor is, after all, just another metaphor – a story we tell to make sense of something we don’t actually understand. And like all the metaphors that preceded it, it will certainly be cast aside at some point – either replaced by another metaphor or, in the end, replaced by actual knowledge.
Misleading headlines notwithstanding, no one really has the slightest idea how the brain changes after we have learned to sing a song or recite a poem. But neither the song nor the poem has been ‘stored’ in it. The brain has simply changed in an orderly way that now allows us to sing the song or recite the poem under certain conditions. When called on to perform, neither the song nor the poem is in any sense ‘retrieved’ from anywhere in the brain, any more than my finger movements are ‘retrieved’ when I tap my finger on my desk. We simply sing or recite – no retrieval necessary.

It's a fascinating and provocative essay. I'd be very curious to hear thoughts on it from writers I follow like Steve Novella (neuroscientist) and George Lakoff (cognitive linguist).

However, there are a few issues that I'd raise with this essay.

The first is that while metaphor is of course not literal — computers don't literally store and process information — metaphors are nonetheless integral to our human process of reasoning. As counter-intuitive as it might be, we literally cannot reason without the use of metaphor. These range from primary metaphors like big is important ("tomorrow is the big day!") or love is closeness ("we grew apart over the last year") and many more, to conceptualizations of time as spatial movement ("the holidays are approaching quickly") or causation as motion ("FDR's leadership brought the country out of depression"). The fact that we conceptualize the brain using the neurocomputational metaphor is not in itself fault, such that it allows us to understand and predict states of cognition. But Epstein is likely correct in that the metaphor is inherently limited. That's why we need a cross-disciplinary study of the mind and brain from neurobiology, neurocomputation, and cognition.

I'm also skeptical of this claim:
[There] is no reason to believe that any two of us are changed the same way by the same experience. If you and I attend the same concert, the changes that occur in my brain when I listen to Beethoven’s 5th will almost certainly be completely different from the changes that occur in your brain.
Our shared biology constitutes a reason to think that responses to similar experiences are at least somewhat the same. Perhaps Epstein simply means that the configurations of neurons that change over a lifetime are inherently widely varied due to our vastly varying experiences; but we don't have to throw the baby out with the bathwater — the same parts of the brain likely undergo similar structural changes in response to similar stimuli, simply because our brains are — by our shared, human DNA — very similar organs.

Those are my thoughts, at least. But it's a provocative topic, certainly.

Full essay: The Empty Brain

18 May 2016

Humans of New York, and thoughts on childhood cancer

Christian theodicies contend that God has a Divine Plan, and thus morally sufficient (if inexorably mysterious) reasons for allowing this child to suffer. (Click to embiggen...)

His story is one of many. If there's anything that convinces me a theistic god — one who is invested in human affairs — does not exist, it's childhood cancer. And the weaselly rationalization that it's a necessary part of God's unknowable, mysterious, yet presumably perfect plan just strikes me as the most blind and desperate kind of faith. 

16 May 2016

Galen Strawson: Consciousness Isn't a Mystery

Galen Strawson, professor of philosophy at the University of Texas at Austin, writes in a New York Times op ed that the "mystery of consciousness" isn't really so mysterious:

Consciousness Isn't a Mystery. It's Matter.

In his own way, he argues for non-eliminative physicalism:

Those who make the Very Large Mistake (of thinking they know enough about the nature of the physical to know that consciousness can’t be physical) tend to split into two groups. Members of the first group remain unshaken in their belief that consciousness exists, and conclude that there must be some sort of nonphysical stuff: They tend to become “dualists.” Members of the second group, passionately committed to the idea that everything is physical, make the most extraordinary move that has ever been made in the history of human thought. They deny the existence of consciousness: They become “eliminativists.” 
This amazing phenomenon (the denial of the existence of consciousness) is a subject for another time. The present point — it’s worth repeating many times — is that no one has to react in either of these ways. All they have to do is grasp the fundamental respect in which we don’t know the intrinsic nature of physical stuff in spite of all that physics tells us. In particular, we don’t know anything about the physical that gives us good reason to think that consciousness can’t be wholly physical. It’s worth adding that one can fully accept this even if one is unwilling to agree with Russell that in having conscious experience we thereby know something about the intrinsic nature of physical reality.

I don't think his take on it is as illuminating as Lakoff's, but for a quick op-ed it does the job.

09 May 2016

Sean Carroll's new book is (apparently at least partly) about model-dependent realism

Salon has an interview with Sean Carroll in which he discusses his new book, The Big Picture, which releases tomorrow (May 10th). Readers of this blog will no doubt be aware of my fondness for Hawking's model-dependent realism or what I consider to be a cognitive-science-based variation, Lakoff's embodied realism. And while I've often referenced Carroll's old blog post about free will as evidence he shares the basic ideas, some of his comments in the Salon interview certainly have a ring about them that should be familiar to anyone versed in those empirically responsible epistemologies:

Naturalists don’t all agree with each other. On the one end of the spectrum you have the most hard-core variety, who claim that only the most deep-down fundamental description of nature can be said to describe something “real.” They might say that consciousness, or morality, or free will, are all just illusions. On the other end of the spectrum you have naturalists who believe in only the natural world, but are willing to ascribe objective reality to various extra properties it might have – moral judgments, for example, or inner states of conscious experience.
Poetic naturalism sits in between. There is only one world, but we have many ways of talking about that world. And if a particular way of talking gives us a useful handle on what the world is and how it behaves, it’s completely appropriate to consider the concepts it evokes as “real.” Air is really made of atoms, but its temperature and pressure are real, even though the individual atoms don’t have temperatures or pressures. Human consciousness and free will are real, even though they’re not present in the individual particles or cells of which we are made.
Whether he ever mentions model-dependent realism by name in the book, I don't know yet (obviously); but he's certainly in the ballpark. Stephen Hawking essentially says that the question of what is 'real' is meaningless; what matters is the utility of a model in its ability to reliably describe and predict phenomena. Lakoff, similarly, suggests that we consider something to be 'real' when it has a theoretical ontology necessary to explain phenomena. I think Carroll is in good company.

18 April 2016

You can't make this stuff up, part who-the-heck-knows

Found on the internet today:
Angels know man and lower beings not according to the mode of the lower beings, but according to the mode of the angelic intellect. God, however, transcends even this and doesn't just know but utterly surrounds and impenetrates all lower being (both "tensed" and "tenseless") with apprehension so as to know them all in an utterly more complete manner, according to the mode of the transcendent, timeless God.
Source (in the comments)

17 April 2016

Bravo, SNL. Bravo.

In one skit, SNL lampoons the Christian persecution complex, their caricature of atheists and 'liberals' in films like God's Not Dead 2: The Undeadening [actual title may vary], and their habit of transparently masking Jim Crow type denial of service laws under the guise of religious freedom. Well done!

14 April 2016

Plato's folk theory of universals

Over the years I've encountered a diverse array of philosophical views across the internet. While my original interest was a/theism, I don't think that nearly ten years ago I could have anticipated just how many related rabbit holes there are and how deep they can go.

One of those is the concept of universals. It's the idea that there's another world 'out there', some metaphysical plane of existence, in which categories-of-things-in-themselves literally exist.

For example, we agree that chairs exists. But what defines a chair? Is a bean bag a chair? What about an ergonomic kneeling chair? What about a tire suspended from a tree branch? Plato would have said that there is an inherent property of chairness that permeates all things that fit within the category chair. Aristotle might have called it the essence of that thing — that which makes a chair a chair.

Color is another commonly cited example of a universal. Grass is green, and so are leaves. According to Platonic thought, grass and leaves are particulars. They are individual objects that are not repeatable — that is, they are discrete. Examples of particulars are generally material objects, but some philosophers take 'immaterial' objects to be particulars as well — sensory data, God, etc. A universal is a property that exists independently of these particulars, but inhabits them. If I burn a patch of grass away, the essence or property of greenness still apparently exists in many other things — and so, Platonic thought teaches, it must be metaphysically real. How, precisely, these universals exist and interact with particulars is a mystery yet to be solved, yet even today philosophers write lengthy books arguing that universals must indeed exist.

For the purposes of this post I'm not going to get into nominalism, realism, and conceptualism — all attempts to account for universals. Are they really 'out there'? Or are they illusory, just part of the mind? Are they just artifacts of language?

If Plato were a psychologist...

My background in studying these kinds of questions is psychology — cognitive psychology in particular. You generally don't hear cognitive psychologists talking about universals or debating nominalism versus conceptualism. That's because cogntive psychologists have been able to study, and answer, the question of whether categories-of-things-in-themselves exist independently of human brains. The answer is no. 

Let's return to the chair. We all agree that chairs exist. But "chair" is a fluid, and even disputed, concept. From kneeling chairs to tires-on-trees to conventional wooden chairs, what we understand a chair to be is dependent on our experience. 
Is this a chair? Is it art? 
This reveals a fundamental problem in the idea that there exists, independently of human minds, a category or essence of chairness. We have a very difficult time defining exactly what it is, what the parameters are that would allow us to uniquely identify the category.

Worse for universals is the fact that categories are often radial. We can, for example, think of a general type of car. We can also think of more specific categories, like particular types of cars. We can do the same for boats, planes, and trains. But we don't have a general categorical image of "vehicle", even though it subsumes all those other categories. Similarly, while we can think of a general concept of a chair, categories of specific types of chairs, as well as other categories of furniture, we can't conceive a representation of the general category of 'furniture'.

The simple answer that cognitive psychology gives us is that while the objects we know as chairs indeed exist outside of our minds (we're not endorsing relativism here), the category of chairs does not. Rather, the category itself is imposed upon the physical world and is inherently a fluid, social construct.

The idea of greenness faces a similar problem. We know from physics that particles of light do not have color. Color cannot be a surface property of objects because some things that are said to have color, like the sky, do not have a surface at all. We know still that a study of the human eye has revealed that we can see only a narrow range of the electromagnetic spectrum, which we call "visible light" — not because it's inherently visible, but simply because it's visible to us. What we call green cannot then be an inherent property of a thing, but rather is a multiplace interactional property that crucially depends on our biology — the interaction of our eyes and visual cortex with the environment. We say that "green" is "real" because we experience it as real, and because others appear to share that experience. But there's no basis to establish the existence of the category of greenness outside of the human experience.

Folk theories versus scientific theories

What's often overlooked in these discussions — particularly since they're steeped in literally centuries of philosophical tradition being pitted against a relatively nascent field of cognitive neuroscience — is that Plato's theory, like Aristotle's theory of essences, is not a scientific theory but a folk theory. Aristotle believed, for example, that the continuity of the self was sustained by an essence that persisted even as our bodies and minds changed. But we now know that the continuity of the self is a product of biology and social construction, and that it can be radically disrupted — as in the case of physical injury to brain that radically alters a person's memory and/or disposition. 

Plato may have thought that his theory was scientific, at least in the sense that it proposed hypotheses that could reliably explain the world around us and our relationship to it. But Plato didn't have access to the structure of his own process of reasoning. He couldn't have possibly known about scientific discoveries in cognition like primary metaphors or overlapping conceptual hierarchies, because those things required empirical study of the mind and brain. The "solutions" of nominalism, realism, and conceptualism are fundamentally solutions to a problem that arose precisely because the concept of universals is a folk theory steeped in metaphorical conceptual systems, and not a scientific theory. 

Unfortunately, ideas like essences and universals persist to this day despite the advances in cognitive psychology that severely undermine them. My guess is that it's going to take some time for centuries (millennia, actually) old ideas still deeply studied in academic institutions to succumb to a competing field. But the reality is that despite all those centuries of debate, philosophers are no closer to resolving these questions than Plato himself was. Instead, we've needed a radical paradigm shift in how we frame and investigate the questions in the first place, and that's why a study of cognitive psychology is critical to empirically responsible metaphysics.