Parables in Philosophy
Parables have their uses and merits in philosophy, even in these desiccated days. They can impart vivid life to elusive abstractions. Plato’s parable of the cave is the most famous philosophical parable, and it is powerfully memorable. It has its defects: notably, the cave wall and the shadows cast on it are just parts of the same empirical world that may be encountered outside the cave—so the cave dwellers are in touch with Reality even while stuck inside the cave. What the lone escapee encounters is just more of the same—perceptible material objects (and there are shadows outside the cave too). There is supposed to be a stark contrast between the world of the cave (empirical reality) and the world beyond the cave (the world of forms), but in the parable the two worlds are made of the same materials. In both places light falls on objects and we see them. Still, one gets the point. The idea is to dramatize the difference between the world of the forms and the world of perceived particulars—the former being more real than the latter. Part of the thought here is that the cave world is more limited than reality as a whole—the cave dwellers are mistaking part of reality for the whole of reality. There is more to reality than they imagine, given the limitations of their experience.
Plato has his parable, his illustrative myth, but where is Aristotle’s countervailing myth? What would be a suitable parable to explain Aristotle’s non-Platonic conception of reality? He rejects Plato’s world of forms, holding that reality belongs to the world of perceived particulars. Without going into elaborate exegesis, Aristotle represents the world of the nominalist or conceptualist—universals are at best reifications of words or concepts. What parable might capture this anti-Platonic position?  The best I have been able to come up with I call “the parable of the tank”, as opposed to the parable of the cave. Here we are to imagine humanlike creatures floating in a tank, a very large tank. Their senses have been shut off, or perhaps they have never had senses (we can tell two versions of the story): they never perceive the empirical world of concrete particulars. However, they hear a voice that is piped into their brains day and night: it is the voice of Socrates speaking to them. They hear nothing else but this disembodied voice; and it is a dulcet and persuasive voice. It speaks lovingly of geometry, of the abstract world, of permanence and perfection, of the Good. It elicits in them knowledge of these things, as with Socrates and the slave boy, and it conveys a reverence for the world of which it purports to speak. The people suspended in the tank fully absorb this discourse—they believe in what the voice of Socrates tells them. They think that the world described by Socrates is the real world; they know nothing of the world of empirical perception, not even suspecting that they are concrete particulars floating in a tank (we can suppose that they can communicate among themselves, and perhaps also with Socrates). In their minds the real is co-terminus with the world described by the voice—basically, the world of Platonic forms. After all, they have experienced nothing else, and the voice has assured them that nothing else is real, even if it might occur to them in a dream. 
But one day one of the tank dwellers escapes: he manages to climb out of his tank and swim to dry land. By some natural magic he is also provided with senses, particularly sight. He sees his first physical objects, he touches them too; he even tastes them. No doubt this is all a great revelation, catapulting him into a brave new world of experience and knowledge. The world is not just the voice of Socrates and those abstract forms; it consists also of concrete solid particulars! At first he is overwhelmed, stunned, even maddened; but he quickly adjusts, concluding that his earlier life in the tank was severely limited—a condition of extreme ignorance. There is clearly much more to reality than he ever suspected. He even entertains the suspicion that this new world is more real than the etiolated world described by Socrates: those vaunted forms were mere shadows compared to these bright and shiny particulars, these solid chunks of matter. He resolves to re-enter the tank and report his findings to the other tank dwellers, wishing to enlighten them. But when he does so he is met with incredulity and derision: the others just don’t believe him, regarding him as unhinged or a con man. And indeed, he can see their point: the world out there has to be seen to be believed—he would not believe it unless he had witnessed it with his own eyes. He finds himself shunned and distrusted, even though he alone is in possession of the truth.
Suppose Plato had taken the teaching of his philosophy to an extreme, equipping his Academy with a special Socratic tank. Since the senses are so misleading, he would abolish them—for they are sources of error and confusion. In the ideal Platonic state education would proceed by installing newborns in the tank, removing their senses, and hooking them up to recordings of the voice of Socrates (don’t ask me how he obtained all this technology). Thus he could inculcate sound philosophy in the minds of the young, later to become the Guardians, without the distractions of the senses: he could educate the polis in the subtleties of Platonism. Let’s imagine he has done this for several centuries, so that Platonism is simply orthodox among the educated Athenian. From Aristotle’s point of view, these tank dwellers are in the same condition of ignorance that Plato diagnosed in his cave dwellers. If one of them were to escape and experience the real world of particulars, he would be treated as a dangerous subversive, or as mad. The parable of the tank, like that of the cave, illustrates the condition of those who cannot recognize the reality of anything beyond their limited experience. And the rhetorical force of the parable is that we can all see that there really is much more to reality than those in the tank suspect—just as we can all see that there is much more to reality than Plato’s cave dwellers suspect.
Aristotle could also appropriate Plato’s parable and turn it against him, by suggesting that the shadows cast on the cave wall might suffice for learning abstract geometry, but that they would not inform the cave dwellers of the world of concrete things that exist beyond the cave. The shadows act as geometrical shapes—circles, rectangles, triangles—and can therefore provide a basis for knowledge of abstract geometrical forms (Euclid would have thrived in this learning environment). But an escapee from this impoverished geometrical world would discover that there is much more to reality than geometrical forms: there is color, weight, hardness, smell, and taste. Plato has described a world in which a single type of form takes up the entire mental space of its inhabitants, but this world is just a small part of all there is in reality—though they, with their limited experience, cannot appreciate that fact. Plato is thus hoist by his own parable.
Here is another parable, inspired by Plato, but designed to make a different philosophical point. We are to imagine a race of beings that live in a black and white world but who have a color projector installed on the front of their head. When they direct their gaze forward the projector sends out a pattern of light that makes the objects around them appear to be colored. There are no colored objects there, but the projector projects colored light onto things (we can suppose that there is no sunlight to interfere). Thus these beings arrive at the belief that they live in a world of richly colored objects, though in fact they do not. The world is less than they suppose, not more; theycontribute the qualities they appear to see in things, not objective reality itself. If they knew about the projector installed on their head, they might question their naïve belief, but we can suppose that they do not. Now one day one of these individuals has a malfunction in his projector (it has never happened before), the result of which is that his world becomes abruptly black and white. Has he become color blind, unable to see what is in front of him? No, he has for the first time seen reality for what it is—colorless. He might investigate the matter and discover the existence of the projector; he correctly concludes that he has been projecting the color all along and mistaking it for reality. He resolves to inform his fellows of his discovery, in the interests of objective truth; but he encounters resistance and hostility—people are reluctant to accept that their familiar world is chromatically impoverished. When he points out the projectors fixed to their heads they insist that these are just ornaments of nature having nothing to do with how they see things. He decides to leave his own projector disabled, in the interests of keeping his perceptions in line with objective reality, leaving others to their fond delusions.
The point of this parable is to dramatize the doctrine of projectivism—about color, clearly, but also about other allegedly projected features of the world (smell, taste, moral and aesthetic qualities, and so on). The mind is our natural projector, tricking us into believing that things that originate with us belong to reality independently of the mind. If the mental projector were to cease to function, we would be confronted by a reality devoid of projections—a thinner and lesser reality. Those who reject projectivism, it will be said, are like the folks in the parable who refuse to accept that they have a projector stuck to their head. Just as Plato’s cave dwellers are by hypothesis ignorant about the true state of things, so these projective beings are by hypothesis ignorant about the true state of things. The parable makes vivid and memorable a philosophical doctrine, contributing to the doctrine’s rhetorical force. They are like those parables in the Bible that dramatize some moral predicament or precept: stories with lessons attached. They aid teaching and comprehension.
 It is true that people, with very few exceptions, are not natural Platonists, so Aristotle is not opposing a natural human tendency, as Plato takes himself to be. But we can imagine a tribe that accepts Platonism from childhood on, as a matter of course: empirical particulars are not real, there are eternal universals existing in a transcendent realm, and so on. Such a tribe might be jolted by a parable that compares them to woefully ignorant people.
 A variant parable might tell of godlike beings dwelling among the forms, contemplating and revering them, but never suspecting that there are such things as particulars that might instantiate them—that concept is alien to their experience. They might be surprised to discover that their pure and beautiful forms compromise themselves by mixing with the tawdry world of transient particulars. Here Platonic heaven functions as the cave: it is a place that limits knowledge.