The transition from the first to the second definition of knowledge in the Theaetetus, is a transition from sensation to doxa as judgement: the second definition does not fail insofar as doxa is conceived of as a form of sense-perception but insofar as human judgement – even in its “pure” and perception-free exercise discussed in the aviary metaphor – cannot meet the standards of infallible knowledge; the example of the jury exhibits the reason of such a failure: the judges of a court are in a position to inferentially form a correct opinion about a fact they have not witnessed to, but this is not infallible knowledge because the latter is a direct grasp of the object. Indeed, it is the directness, rather than the sensible grasp, what matters in the jury example (which clearly alludes to the theory or recollection). Perception is direct grasp, but not of the “right object”; human, embodied thought has the right object but does not have a direct hold on it, as true knowledge is supposed to have.
The advantages of the dialogical form seem to be beyond question as far as its aim is persuasion. But is the aim of dialogue persuasion only? Or, rather, does philosophical inquiry, though dialogical in form, also have the goal of demonstration? And if this is so, how can we justify a choice which clearly seems to favour the goal of persuasion over the goal of demonstration? And – finally – even if philosophy, according to Plato, cannot avoid taking part in persuasion, is there a way of granting to it also a demonstrative character? What distinguishes Platonic persuasive philosophy, on the one hand, from the mere persuasion which rhetoricians and sophists (of all times) aim at is not primarily a matter of theory. The dialogical method fragments the theory into the different characters, according to their attitudes and peculiarities. What sets the Socratic dialogue beyond the mere singularity of the characters, and thus turns it into something more than a simple matter of persuasion, consists in the fact that it starts from universally compelling questions and looks for answers tailored precisely to them. The persuasion created by sophists and rhetoricians, by contrast, is unstable and unreliable, firstly because the problems they raise are casual and far from pressing or compelling for human life; secondly, because even if sophists and rhetoricians manage in some way to discover the right problems, their answers are totally off-target, unresponsive both to the depth of the questions and the extent of their implications.