Well, let me just lay out Plato's story about true and false arts without getting slowed down by the rather lengthy dialectical back and forth of the conversation. One must not take this "theory" too seriously. I have always imagined that Plato was so quick and so smart that schemata like this one simply popped into his head all the time. His underlying thesis is deadly serious, but he is not above having some fun along the way. So, here goes.We can distinguish between the body and the soul [psyche, in Greek, which can better be translated "personality" but never is. Inasmuch as the early Church Fathers incorporated Platonic and neo-Platonic metaphysics into their theology, we can never really completely filter out the religious connotations of "soul" from the moral psychology Plato intended. Just one more thing to blame religion for, I guess.] In the case of each of these, there is an art that is devoted to maintaining the health of its object, and a sister art devoted to restoring that health when it has for some reason been lost. Socrates suggests that gymnastic is the art of maintaining the health of the body [the Athenians were of course fanatic about working out], and medicine is the correlative art of restoring physical health when it has been lost. Remember the three-part analysis of arts, or technes, sketched above. The object on which both gymnastic and medicine work is the body. The goal at which both aim is the good of that object, namely physical health. And each art is guided by a body of rational knowledge about its object.
It is not really very clear what exactly the body of rational knowledge is that the physical trainer or the doctor possesses. In Plato's day, very little was actually known about the functioning of the body. Furthermore, it is central to Plato's serious argument that the knowledge on which the art rests includes, as an integral part of it, normative truths about the good of the object. I suppose this has a certain plausibility in the case of medicine. Even the diabolically evil doctors who performed their hideous experiments on Nazi death camp inmates had, I imagine, the same professional notion of what constitutes a healthy liver or heart or lung as normal doctors. But very shortly, Plato is going to extend this notion of health to the soul, or psyche, and at that point, he is going to need more than an analogy to make his case.
But I get ahead of myself. For each of the true arts of the body -- gymnastic and medicine -- there corresponds a false art, or knack, a kolakeia. This is distinguished from the true art both by the goal at which it aims and by the doxa, or belief, with which it operates. At this point, Plato invokes the distinction on which so much of his philosophy rests, a distinction that he bequeathed to the entire western philosophical tradition -- the distinction between appearance and reality.
The false arts, or knacks, of the body aim at the apparent good of the body, not at its true good. Corresponding to gymnastic, which aims at the reality of physical health, is the knack of cosmetics, which aims at the appearance of health in a body that may in fact be sick. With creams and paints and such, it contrives to make a sick body look healthy. What is more, cosmetics uses guesses and old wives' tales and mere empeiria -- habitual nostrums grounded in no genuine knowledge of the true functioning of the body [Hey, I am just expounding Plato here -- I don't want any grief from devotees of Helena Rubenstein!]
Corresponding to medicine, the true art of healing the sick body, is cookery, the knack of producing pleasant tasting confections that fool the body into thinking it is being healed, when in fact it is just being flattered and petted and momentarily pleased. [Think here of the weight loss advertisements that promise that you can lose thirty pounds while still not giving up the ice cream and pizza you love.]
What then are the true and false arts of the soul? Perhaps not surprisingly, Plato identifies these as political or public arts, rather than as private or personal arts. Plato, we should remember, seems not to have believed that a person can be truly just when living in an unjust society. The true art of maintaining the health of the soul, which we may think of perhaps, as the health of the "body politic," is legislation. The proper ordering of the laws and statutes of a city-state will serve to maintain the moral or, in a certain sense, spiritual, health of its residents. But when a person [presumably, a man, although see The Republic] has become, as it were, morally unhealthy, by committing acts of injustice, then it is necessary, however painful, to invoke the art of restoring moral health, namely the system of justice. [In the absence of anesthetics and such, medicine was unavoidably a very painful process for the classical Greeks, so the analogy between medical treatment and judicial punishment seemed quite natural to Plato.]
Well, what are the false arts of the soul, corresponding to cosmetics and cookery? [By the way, I just recalled that the offending line in my limerick was "cookery and quackery and all sorts of knick-knackery." Not too bad, really.]
The false art, or knack, corresponding to legislation, Socrates says, is sophistic, which is aims at making the body politic appear morally healthy when in fact it is not. Plato is thinking here of the popular democratic politicians, like Pericles, whose skillful use of meretricious argument seduced the Athenian people into disastrous wars. This sophistic is the knack of getting the Athenian people to embrace unwise and harmful [politically and morally unhealthy] policies, which feel good but in fact leave the city-state weaker than before.
And finally -- this is the point of this entire exercise -- what is the false art or knack corresponding to justice? It is the knack of evading necessary and morally curative punishment in the law courts for misdeeds, by fine speeches that are utterly divorced from knowledge of the true good of the psyche. In short, rhetoric. So, rhetoric is the cookery of the soul!
Agree or not, you have to give it to Plato. This is a simply wonderful send-up of Gorgias' pretentious claims for his "art" of rhetoric. "You are no better than a pastry chef!" Socrates tells him. Well, Plato has had his fun, and the dialogue now turns a good deal more serious, giving Plato the opportunity to introduce one of his most controversial theses -- a thesis, furthermore, that gets fully explored in the Republic as well as here in the Gorgias -- I refer to the paradoxical claim that the absolute tyrant is the least powerful of all men, despite his ability to put to death anyone he chooses.