Socrates' discussion with Meno begins as Meno asks whether virtue can be taught. Meno suggests that it may be a result of practice or an inherent trait. Socrates answers by reminding Meno that Meno's own countrymen, the Thessalians, have recently gained a reputation for wisdom, due chiefly to the rising fame of Gorgias (a Sophist teacher). Gorgias, Socrates says, has taught people "to give a bold and grand answer to any question you may be asked, as experts are likely to do."
Athenians, on the other hand, do not claim to be able to answer such questions, says Socrates, noting that he himself is certainly among the ignorant. We should note that Socrates' modesty here is somewhat false, at least in the context of the dialogue that is to follow. For Socrates (and for Plato), it is much better to know that one does not know than "boldly and grandly" to claim knowledge when one is in fact ignorant. Thus, Socrates' modesty simply sets up Meno, the Thessalians, Gorgias, and the Sophists in general for a fall later on in the elenchus.
Socrates adds to his admission of ignorance the statement that he has not yet met anyone who knows what virtue is (though he qualifies this statement with regard to Gorgias, claiming not to remember his meeting with him clearly). This claim astonishes Meno, who moves quickly, at Socrates' behest, to give a definition of virtue. Meno says that there are different virtues for men (managing public affairs, helping friends, harming enemies, and protecting oneself), for women (managing the home, protecting possessions, and being submissive to one's husband), and for children, slaves, the elderly, and so on.
This, of course, is not a definition but a list of different kinds of virtue. Socrates points this error out with a metaphor about Meno's "swarm" of virtues being like a swarm of bees. The bees differ in size and shape, but "do not differ from one and other in being bees." In other words, Socrates is after the definitive characteristics of virtue in general, the "form" (eidos) of virtue. This idea of forms, which suggests that there is an ideal, non-physical model for each kind of thing, will eventually play a major role in Plato's dialogues. Here, the term is used sparingly, and Plato seems to be thinking of forms as somehow inherent in each physical thing rather than as separated in some mental or divine realm.
In addition to the bees metaphor, Socrates also uses qualities like health and strength to show Meno that he is asking after the single form common to all kinds of virtue (strength in a man, for example, is the same thing as it is in a woman, regardless of how much of it is present).
Meno, however, is still somewhat unsure what Socrates is getting at. This persistent confusion should remind us of the originality of Socrates' and Plato's thought at the time (ideas that are now commonplace to us). The idea that the term "virtue" must refer to one thing in all of its individual examples (i.e., the idea of a definition) is quite different from the ancient Greek conception of virtue as various kinds of success in worldly affairs.
Socrates reminds Meno that no virtuous quality is any good without "moderation and justice." Meno agrees, and Socrates points out that this idea gets at something common to all cases of virtue. Meno seems to understand this and makes a second attempt to define virtue: "What else" is it, he asks, but "to be able to rule over people?"
This definition is immediately thrown out, however, as Socrates reminds Meno that ruling over others is not virtuous in slaves or children. In any case, Socrates asks, shouldn't Meno have added "justly and not unjustly" to the phrase "ruling over people?" Meno agrees, noting that "justice is virtue." Socrates takes that statement as an opportunity to make a further point about definitions: does Meno mean that justice is virtue or that it is a virtue?
Meno, however, still fails to grasp this distinction between instances of virtue and the definition of virtue, and Socrates must use another example. Roundness, he notes, is a shape, but is not shape itself. Meno again seems to grasp the difference, and clarifies his statement about justice: it is a virtue, not virtue itself. "There are many other virtues," he says, and he goes on to list some of them ("courage...moderation, wisdom, and munificence, and very many others").
This third attempt by Meno to define virtue contains, of course, the same mistake as his first attempt. Socrates notes that they have again "found many virtues while looking for one." Meno again professes confusion, and Socrates again resorts to the example of "a shape" versus "shape" in general. He also mentions color in the same regard.
Meno, however, simply asks Socrates to answer his own question and define "shape" and "color" himself, so that Meno will have an example to follow in defining virtue. This turning of the tables, in which Socrates' interlocutor asks him the questions, is a relatively rare occurrence in Plato's dialogues. Here, it serves to give Plato the opportunity to contrast Socrates' style of definition with that of the Sophists.
Socrates, after making sure that Meno knows the geometrical terms "limit" and "solid," defines shape as "that which limits a solid; in a word, a shape is the limit of a solid." Then, after chastising Meno for ordering him around, Socrates proceeds to define color "after the manner of Gorgias" (rather than after his own manner, in which he defined shape). He mentions Empedocles' concept of effluvia, those elements that travel into us via our sense organs and allow us to sense the external world. Using this concept, and quoting Pindar along the way, Socrates defines color as "an effluvium from shapes which fits the sight and is perceived." The main contrast highlighted here is between Socrates' simple, direct account and the "theatrical" accounts of Gorgias and the Sophists (which are full of high-flown theories and quotations).
In return for these definitions, Meno makes a fourth attempt at defining virtue: using a literary quote (in true Sophist style), he says that virtue is "to desire beautiful things and and have the power to acquire them." Like his idea about virtue as the power to rule, however, this definition is quickly broken down by Socrates' questions. Socrates points out that some men desire bad things, and further that they do not know these things to be bad (since no one desires what will harm them). "What else is being miserable," he asks, "but to desire bad things and secure them [for oneself]?"
Meno's most recent definition, then, amounts to virtue as "the power of securing good things." Even this is not enough for Socrates, however, who points out that the acquisition of good things is only good if it is done "justly and piously" (otherwise such acquisition is "wickedness").
But now Socrates and Meno are back to square one, having stumbled into another error with regard to the nature of a definition. If virtue is to acquire good things justly, and if justice is a kind of virtue, Meno has simply repeated his earlier mistake of using kinds of virtue to define virtue itself. This mistake, however, is slightly different from the earlier mistake in which Meno defined the thing simply by listing its instances. Here, Plato is also showing us that a definition cannot contain the term to be defined--one cannot give a definition of virtue as "virtue" or as "that which is a part of virtue."
Meno, at the end of his rope, calls Socrates a torpedo fish (a fish that numbs whatever touches it). "Both my mind and my tongue are numb," he says. Though he has "made many speeches about virtue before large audiences on a thousand occasions...now [he] cannot even say what it is." This state of coming to know that one does not know is typical of Socrates' method in Plato's dialogues, and is known as aporia.