Richard Kraut's excellent article, "Plato", in the Stanford Encyclopedia of Philosophy, includes a section, "Does Plato Change his Mind About Politics?", which raises some good questions about method. Kraut writes:
Just as any attempt to understand Plato's views about forms must confront the question whether his thoughts about them developed or altered over time, so too our reading of him as a political philosopher must be shaped by a willingness to consider the possibility that he changed his mind. For example, on any plausible reading of Republic, Plato evinces a deep antipathy to rule by the many. Socrates tells his interlocutors that the only politics that should engage them are those of the anti-democratic regime he depicts as the paradigm of a good constitution. And yet in Laws, the Athenian visitor proposes a detailed legislative framework for a city in which non-philosophers (people who have never heard of the forms, and have not been trained to understand them) are given considerable powers as rulers. Plato would not have invested so much time in the creation of this comprehensive and lengthy work, had he not believed that the creation of a political community ruled by those who are philosophically unenlightened is a project that deserves the support of his readers. Has Plato changed his mind, then? Has he re-evaluated the highly negative opinion he once held of those who are innocent of philosophy? Did he at first think that the reform of existing Greek cities, with all of their imperfections, is a waste of time — but then decide that it is an endeavor of great value? (And if so, what led him to change his mind?) Answers to these questions can be justified only by careful attention to what he has his interlocutors say. But it would be utterly implausible to suppose that these developmental questions need not be raised, on the grounds that Republic and Laws each has its own cast of characters, and that the two works therefore cannot come into contradiction with each other. According to this hypothesis (one that must be rejected), because it is Socrates (not Plato) who is critical of democracy in Republic, and because it is the Athenian visitor (not Plato) who recognizes the merits of rule by the many in Laws, there is no possibility that the two dialogues are in tension with each other. Against this hypothesis, we should say: Since both Republic and Laws are works in which Plato is trying to move his readers towards certain conclusions, by having them reflect on certain arguments — these dialogues are not barred from having this feature by their use of interlocutors — it would be an evasion of our responsibility as readers and students of Plato not to ask whether what one of them advocates is compatible with what the other advocates. If we answer that question negatively, we have some explaining to do: what led to this change? Alternatively, if we conclude that the two works are compatible, we must say why the appearance of conflict is illusory.The view that the Republic and Laws could not possibly conflict is surely ridiculous--and something of a red herring. It's what Kraut says after considering that view which is truly important (hence the emphasis). That passage, I think, makes one valuable point, but also suggests something which I think is not correct.
The valuable point is that, in developmental studies, one must first establish that there is a change (that is, an incompatibility or inconsistency of views across time), before attempting to give an explanation of it. The change is the explanandum; one's developmental theory is the explanans. In this regard, one might also wish to emphasize that it's of crucial importance to state the change correctly. For instance, I think it is not correct to say, without qualification, that Plato is 'opposed to rule of the many' in the Republic. Rather, he thinks that ignorant people should not have political authority just because of their numbers, and he also thinks that political authority is a burden not a benefit, to be avoided if possible. That presumably has to be included in the explanandum, not 'opposition to rule of the many.'
The incorrect suggestion (it's a suggestion only, not an explicit claim--the suggestion comes from the nearness of the ridiculous view that has been rejected) is that, when there is an appearance of incompatibility, the person who in the end wishes to deny it, and the person who in the end wishes to affirm it, are on equal terms. (Kraut's way of putting it suggests that, either way, one 'has some explaining to do.')
Rather--and of course-- the presumption should be in favor of compatibility, within a work as well as across works, and the burden of proof falls on the person who wishes to affirm incompatibility. The reason for this is that apparent inconsistencies arise all the time in our reading of any interesting philosopher, and a presumption of consistency prevents us from continually stalling in our progress to understand.