The dialectic is Plato’s name for his philosophical method that proceeds in part by what many commentators call the method of hypothesis. Previously I have discussed how Plato’s method can’t quite live up to his own standards. The problem stems from that fact that Plato’s claim that we have direct intellectual access to the forms, which partially justifies the method’s correctness, is demonstrably false. Even upon rational reflection and lifting our minds away from the material world people still disagree about what things such as good and justice are. Which proves either that we don’t have an error-free way of getting at the forms, or that we are reaching out to different forms under the mistaken belief that we are both grasping the same form of justice. Both are disastrous for Plato because we are thus unable to produce truths about justice via that intellectual access (since are either unable rule out mistakes or to be sure that the truths are about justice and not something else). But this is simply to reveal that Plato’s rationalism, his belief that the intellect alone can arrive at truths about things such as justice, is flawed. Here instead of focusing of Plato’s method as Plato’s method I am simply going to examine it as a method and examine its strengths and weaknesses, what it can and can’t do.
Allow me to first describe the method of hypothesis, one half of the dialectic. I claim that the method of hypothesis is only part of the dialectic because it is shared with what is called the dianoetic method by Benson. To explain the difference between the two I must describe briefly a distinction Plato makes within ideas themselves. One kind of ideas are those that correspond to the sensible world (such as mental descriptions of the world, or even complete fictions), the other kind of ideas are those that are completely abstract and are related only to other ideas rather than to the world. When dealing with both kinds of ideas the method of hypothesis is employed, according to Plato, but when we deal with the second kind (and it is working with this kind of ideas that lead to knowledge) we not only use the method of hypothesis but proceed on the basis of those hypotheses to the “unhypothetical first principle of everything.”
Setting such distinctions aside for the moment, the method of hypothesis can be compactly described as putting forward hypotheses (statements whose truth we do no know) and then investigating the consequences of that hypothesis in order to determine its truth. The method of hypothesis, construed so broadly, makes the scientific method an example of it in practice. In the case of the scientific method the hypotheses are confirmed or disconfirmed through the evidence of our senses, but even if Plato’s method for philosophy was broad enough to include this it is clearly not how he intended it to be employed, or how he employed it himself. One reason that Plato might be moved to reject hypothesis is because they are internally inconsistent, and certainly we would agree with such a principle today, since it is the essence of the reductio ad absurdum. But Plato rarely has such an opportunity to demolish a hypothesis, usually it is the case that the hypothesis is rejected because it conflicts with some other claims believed to be true. If this really is how we are to reject hypotheses then the method faces a number of difficulties. First of all these other beliefs are not usually themselves empirical facts (which is why this process is not identical to the scientific method). Why then should we consider these pre-existing beliefs more likely than the hypothesis? Because clearly from the knowledge we gain by this method we may arrive at conclusions, such as that justice is better for us than injustice, which may themselves contradict our pre-existing beliefs. But let us be generous and allow that these beliefs are restricted to those that are common sense, which we are absolutely sure of. Given that what prevents us from, upon finding a contradiction with such a pre-existing belief, create a new hypothesis that is the same as the old hypothesis plus the additional claim that the belief that was in conflict is false? Proceeding in this way we can, starting with any hypothesis, generate a hypothesis that includes the original as a sub-claim and which is not in conflict with any claims not under consideration as part of the hypothesis. Of course we may simply stipulate that no hypothesis may contradict any beliefs that are admitted into the set of beliefs that are considered common sense. But this raises an additional problem, namely that the negation of many interesting philosophical hypothesis may simply be considered common sense by some, and thus may be ruled out, to our dismay. For example, Thrasymachus may consider the claim that justice is to the advantage of the rulers to be common sense, and thus that any hypothesis which contradicts this, including Plato’s later conclusions about it, can be immediately dismissed by him. And finally there is the problem that neither of two competing hypothesis may come into contradiction with our existing beliefs; certainly there is nothing that prevents this from happening. Since we also accept the principle that both such hypotheses can’t be true (since accepting both would lead to internal contradictions) we must pick one, but the choice seems completely arbitrary.
Thus, as put forward by Plato, the method of hypothesis seems, at least by itself, best suited to some kind of common sense view of philosophy. Such an approach entails understanding the purpose of philosophy not as to produce truths but simply to produce claims that agree with our other beliefs, and possibly to iron out any disagreements in our existing beliefs. As such this approach does not take issue with the inability to challenge our existing beliefs, unless such challenge is motivated by another of our existing beliefs, nor does it find the possibility of being able to endorse two competing hypotheses as a problem. Since we are not trying to produce philosophical truths either hypothesis will do just as well as the other, given that they agree with our common sense beliefs. Although it is not my purpose to thoroughly criticize such an approach to philosophy let me quickly mention the two most significant problems with it: first that it makes philosophy hardly worth doing, and secondly that trying to ensure logical coherence is something that only matters when we are after the truth or something very much like it, and thus that the method is inconsistent with its purported aims.
With this description of the method of hypothesis out of the way we can turn to what separates the dialectic from the dianoetic. Plato implies that it is a failing of the dianoetic that it never directly supports the hypotheses themselves. In some ways then Plato seems sensitive to the criticisms described above, and it is perhaps because of them that the dianoetic method is considered weaker. Plato seems to be implying that what we are supposed to do is from our hypotheses form further hypotheses such that these new hypotheses (fewer in number) entail our old ones, and that we are to continue this process until we reach a single “unhypothetical first principle of everything.” Unfortunately what this entails exactly, and why the unhypothetical first principle does not itself need some kind of support, is left unexplained. In fact Plato himself implies that he fails to completely follow his hypotheses back to the first principle in his dialogues. It is possible, however, to interpret Plato’s argument in the Republic as an example of at least part of this process, where on the basis of initial hypotheses we advance to more fundamental hypotheses, although we stop short of the first principle itself. Plato begins his investigation by hypothesizing that the best city is one that fulfills our needs (and he describes the city that does this in great detail). And to justify that hypothesis he hypothesizes that good things are properly those that are functioning properly (although he does not explicitly state this as a more fundamental hypothesis). This implies that the city is good (because of its functioning well), and that the things that enable it to function well are its virtues (wisdom, courage, temperance, and justice). But this is not exactly an unproblematic example. Certainly it seems that we might easily construe the claim that what allows the city to function well are its virtues, that wisdom, courage, temperance, and justice are virtues, and that the function of the city is to serve our needs, as additional hypotheses unjustified by the more fundamental hypothesis. Indeed in general it is usually the case that to justify a hypothesis requires more hypotheses, not a single more general principle. Now we could construe what seem like additional hypotheses as simply definitions (self evident by virtue of understanding the meaning of the words), but what makes them definitions rather than hypotheses is not exactly clear (besides our desire to make Plato’s method cohere with his use of it). And thus I must end this discussion of Plato’s method as a method for philosophy here because I cannot properly comment on the dialectic as distinct from the dianoetic and what kind of approach to philosophy that method fits best with, because I cannot clearly grasp what exactly that method is or how we are supposed to use it.