After the debunking of the definition of temperance as "doing our own business," Socrates begins to suspect that Critias (who appears increasingly agitated) was the original source of the definition. Socrates asks Charmides if he thinks that the person who invented the definition understands it, and proceeds to ask Critias, who is older and more educated, if he would like to try and defend it. Critias agrees. (Here the dialogue form continues, but Critias says much more in his replies than Charmides did in the previous section.)
Socrates continues to argue that craftsmen, for example, make and do things not just for themselves, but also for others, and they can nonetheless be temperate. This presents a problem for the definition of temperance as "doing our own business." Critias replies that craftsmen making something for others is not the same as craftsmen doing something for others. He quotes Hesiod in saying that "work is no disgrace," and argues that, while a worker might do something intemperate, they will remain temperate insofar as what they make is noble and useful. Their work, then, is their own business insofar as their work is useful and noble, and only this kind of noble manual work can truly be called "doing." When men make something that is not so noble or useful can they be said to be doing the business of others.
Socrates objects to Critias's unclear, nitpicky distinctions between doing, making, and working, and asks him to describe more clearly the thing (doing, making, or whatever) by which he would define temperance. Socrates says that it seems that Critias has claimed that doing good (and not evil) is temperance. Critias agrees. Socrates briefly develops this definition to include the stipulation that temperance lies in doing good both for one's client and for oneself (so that the temperate physician benefits both his patient and himself). He then suggests that craftsmen and physicians do not always know when their deeds will benefit both themselves and their clients. In that case, one can be temperate without necessarily knowing it.
Critias objects to this last formulation, withdrawing whatever concessions he has made that would now require him to say that one can be temperate without knowing oneself. For this self-knowledge, he says, is in fact the "essence" of temperance. Critias cites the Delphic oracle's commandment, "Know Thyself," as evidence here, arguing that the statement is nothing less than the gods' greeting to humans and not a simple piece of advice. This command-in-greeting, he argues, is a riddle that means nothing other than "be temperate." Critias proposes that they drop the former, useless argument, and he will now try to defend the definition of temperance as self-knowledge.
Socrates reminds Critias that he (Socrates) doesn't come to these questions with prior knowledge, but that he is rather inquiring after knowledge. After pausing to reflect, Socrates proposes that temperance, if it is a kind of knowledge, must be a science. Critias replies that it is the science of a man's self. But if each science produces a good effect (as medicine, the science of health, produces health, and architecture, the science of building, produces houses), asks Socrates, what good effect does temperance, the science of a man's self, produce?
The dialogue takes a fairly drastic turn at this point, as Charmides and Socrates both subtly agitate Critias (who invented the definition they had just thrown out) until he can't help but jump in and argue. Charmides, then, seems simply to evaporate, and the conversation becomes both more serious and less animated by trickery, flirtation, or desire. Critias, as Socrates notes, is significantly more educated than Charmides, and he appears to have devoted much more time to thinking about these philosophical issues than Charmides. In a sense, then, Plato has sent Socrates to "level two" of the debating game. This move happens fairly often in the early dialogues; we are eased into the elenchus by a younger, more naive interlocutor (in the Lysis and the Charmides, this is the beautiful youth) before we hit the more serious discussion.