If the purpose of a prelude is to give inducements to follow the law, then why should Plato use the analogy of free and servile doctors to illustrate that point? Wouldn’t some less elaborate comparison serve equally well—say, likening a true legislator to a caring father or mother (which Plato does elsewhere)?
The analogy seems well enough explained simply by the constraints Plato has set for himself. He wants an example, of some single domain in which persons give commands or orders, but in which there is a clear distinction between those who merely threaten to punish disobedience, and those who additionally give inducements for obeying. Parents would not illustrate the contrast well, because no parents merely threaten, or, those who do this can't easily be picked out.
It's interesting that Aristotle, when apparently aiming to draw a comparable distinction (NE 1060b24-32), resorts to the somewhat exotic example of Persian households to make his point:
h( me\n ga\r patro\j pro\j ui(ei=j koinwni/a basilei/aj (25) e)/xei sxh=ma: tw=n te/knwn ga\r tw=| patri\ me/lei: e)nteu=qen de\ kai\ (/Omhroj to\n Di/a pate/ra prosagoreu/ei: patrikh\ ga\r a)rxh\ bou/letai h( basilei/a ei)=nai. e)n Pe/rsaij d' h( tou= patro\j turannikh/: xrw=ntai ga\r w(j dou/loij toi=j ui(e/sin. turannikh\ de\ kai\ h( despo/tou pro\j dou/louj: to\ ga\r tou= despo/tou sumfe/ron e)n au)th=| pra/ttetai. au(/th me\n ou)=n o)rqh\ fai/netai, h( Persikh\ d' h(marthme/nh: tw=n diafero/ntwn ga\r ai( a)rxai\ dia/foroi.
The relationship of a father to his sons is similar to a kingship, since a father has a concern for his sons. ... The reason is that the intent of a king's exercise of authority is to be like a father's. But among the Persians the father is like a tyrant in how he exercises authority, since (i) he treats his sons as slaves, and (ii) a master's exercise of authority over his slaves is like that of a tyrant. (Why? Because it works out for the master's advantage.) That seems correct, to be sure, but the Persian way of doing things is misguided, because when the subjects differ, the exercise of authority also differs.
But why doctors?
It's not simply doctors: it's doctors and also athletic trainers, as we've seen. Plato of course frequently likens virtue to health, and both medicine and physical training take health as their goal, in the sense that the first restores it, and the second preserves it. But this leads to another important point. Plato apparently wants an example in which the really crucial thing is to carry out the command--when, if we agree with what the other person is saying, but don't do what he says, then there is no benefit to us. Plato wishes to emphasize through these examples that people become virtuous only through doing what the law commands.
Compare here also Nicomachean Ethics:
Most people don't actually act on these things, but they take refuge in discussion, and presume that they're 'philosophizing' and that they'll become good persons in that way--carrying on in much the same way as sick people who pay careful attention to what their doctors say, but don't carry out anything they've been ordered to do. Well: these people aren't going to get better in their bodies through that sort of therapy, and neither with those get better in their souls, if that's their way of 'philosophizing'. (1105b12-18)
a)ll' oi( polloi\ tau=ta me\n ou) pra/ttousin, e)pi\ de\ to\n lo/gon katafeu/gontej oi)/ontai filosofei=n kai\ ou(/twj e)/sesqai spoudai=oi, o(/moio/n ti poiou=ntej toi=j (15) ka/mnousin, oi(\ tw=n i)atrw=n a)kou/ousi me\n e)pimelw=j, poiou=si d' ou)de\n tw=n prostattome/nwn. w(/sper ou)=n ou)d' e)kei=noi eu)= e(/cousi to\ sw=ma ou(/tw qerapeuo/menoi, ou)d' ou(=toi th\n yuxh\n ou(/tw filosofou=ntej.
(Note that this passage seems to suggest that 'philosophizing' can have a derisive sense, to indicate someone who is 'merely spouting gas', that is, talking and talking, when decisive action is required. But then--one might wonder--is that the sense in which the slave-doctor uses the term at Laws 857c, when he accuses the free-doctor of 'coming close to philosophizing'.)
Doesn't Bobonich emphasize these things also in his interpretation?
It seems he does not. Plato insists that a mark of virtue is obedience to law: he even entertains the thought that a person's proven willingness to live in subjection to the commands of law should serve as the sole qualification for political authority (715c). But Bobonich seems suspicious of the imperative character of law. Bobonich takes the very fact that law issues an order to be 'savage'. For law to issue a command, Bobonich says, is a failure of the law; it is a declension from the purest and best sense of law, which would involve only persuasion: "law here is seen as violent not only insofar as it threatens a penalty, but also simply in virtue of issuing a command with no explanation"(97).
Although Bobonich correctly emphasizes that Plato wishes to identify reason and law (and also reasonability and lawfulness), there is a deep divergence, I believe, in how they conceive of reason. For Plato--and this I think is a constant theme in his philosophy--it pertains to reason essentially to impose order. When rational beings are involved, this imposition of order would take the form of the issuing and accepting commands. But it seems that for Bobonich, in contrast, reason is (as we might say) deliberative solely--any imposition of order by someone, upon a reasonable being, would be a violation of the autonomy of the latter: "There are aspects of Plato's thought that suggest a striking concern for freedom and autonomy. As we have seen, the appeal to the idea that Magnesia's citizens deserve to be treated as free people and benefit from such treatment is at the heart of Plato's justification of preludes in the Laws" (Plato's Utopia Recast, p. 203, section on 'Autonomy')
But isn't it true that Plato, like any masterful writer, often makes use of a single device for a variety of purposes. Might the free/servile doctor analogy serve the purposes you've just mentioned, but also the larger purpose of illustrating the kind of lawfulness that is appropriate among free and equal persons? Plato does say that free doctors will tell their patients some reasons for the treatment, and legislators similarly.
Presumably any larger purpose the analogy might serve should be judged from its immediate context in the dialogue. But what do we find when we look at the text? In the immediate neighborhood preceding 720a, we find three chief themes:
1. It would be better if the gods ruled over us, as in the time of Cronus, but, failing that, reason should rule, which is the imposition of a divine order (713c-d).
2. Human beings have inherently expansive desires for power, fame, wealth, and pleasure. We want 'as much as possible' of all of these things. To accede to these desires is to be vicious; to put a check on them, through subjection to law, is to be virtuous. (Here we see another theme which is a constant in Plato: that virtue and sobriety, swfrosu/nh, are one and the same.) (715b-c)
3. Thus, when one human being rules over another, and imposes some limit on the actions of another, the person on whom this imposition is made may legitimately wonder whether he is being limited so that the other can further satisfy his lust for wealth, pleasure, etc. (whence the maxim, "Justice is the advantage of the stronger"), or he is being limited in his action, because the ruler is imposing order in accordance with a divine order, for his own good (714c).
But this then would explain the other features of the analogy, especially the idea that a doctor might induce compliance by teaching: Given the three themes above, it is clear that a ruler would have better success in getting citizens to obey the law, if he made it plausible that the laws he promulgates impose limits on citizens for the advantage of the citizens, and as an extension of the divine order.
That is, the free/slave doctor analogy may be explained well enough--and elegantly and conservatively--simply by drawing on material which precedes the introduction of that analogy.
But it was conceded yesterday that sometimes "we become capable of seeing the upshot of a passage, only when it is placed in the proper, overall context." Bobonich puts forward an attractive ideal of the sort of authority that suits free and equal persons. When this ideal is placed beside Plato's discussion, doesn't it serve to illuminate what Plato is saying? But if it does illuminate in that way, can't we say that, at some deep level, Plato is striving to articulate that ideal?
It's hazardous to interpret a text in that way, since, without some suitable restriction, any text could be interpreted as meaning almost anything.
The restriction I would favor is this: that the principle or ideal, which one claims can serve to illuminate a text, must have some antecedent probability of actually being held by the author. (I take this phrase, 'antecedent probability', from Newman, who takes it from Butler.)
Bobonich's proposes that Plato holds the principle that "it is ethically appropriate that [among two free and equal persons] one try as far as possible to persuade the other rationally; because of the patient's status as a free person, he deserves to be rationally persuaded" (105). Bobonich agrees that this is a principle of autonomy. Without getting into unnecessary disputes about precisely how the principle is to be phrased or understood, it is clear that it belongs in that broad class of principles of autonomous self-rule, of the sort that one finds in Rawls and Kant. Its import, broadly, is that all rule is self-imposed; that there is no legitimate authority except that which derives from (not simply 'depends upon') the consent of the governed; that political authority is inherently coercive and that it can be justified only as in accordance with reasons that someone subject to that authority already accepts.
In my view there is little, if any, antecedent probability of such a principle being held by Plato. This is so because of various broad features of his thought, such as his understanding of the virtue of piety; his view that merely begetting someone establishes a claim of authority (690a ff., recapitulated, tellingly, at 714e); that knowledge similarly establishes such a claim; his notion of rationality as the imposition or order (already cited); and his view that government is onerous, and that it would be better if the gods ruled us. Furthermore, as a matter of the history of political thought, principles of autonomy seem to be relatively recent formulations: perhaps such a principle is implicit in Rousseau, definitely it is in Kant--but what are the grounds, antecedently, for expecting to find such a principle inPlato?
Yet if there is little or no antecedent probability that Plato actually held such a principle, then the fact that it illuminates passages does little to establish that Plato was in fact proposing it.