Having disposed of Simmias' argument, Socrates now turns to Cebes' objection. Socrates finds Cebes' argument very compelling, and acknowledges that in order to answer it, he will have to discuss in detail the reasons for generation and destruction. Socrates offers to describe his own experiences in this connection in order to elucidate the discussion somewhat.
When Socrates was younger, he recounts, he had a passion for the natural sciences. He was intent on learning what caused things and their attributes to come to be, to cease to be, or to continue to be. However, Socrates soon came to the conclusion that he was not right for this sort of inquiry: his speculations so confused him that he began to unlearn everything he had previously thought he knew. For instance, Socrates no longer knows even how to give an account of how one and one equals two. He finds it hard to believe that the reason for their becoming two is simply the fact that they were brought together. Nor can he believe that when one is divided in two, the reason for its becoming two is the division. In the first case, one becomes two through addition, in the second case, one becomes two through division: how can both addition and division be the reasons for one becoming two? Utterly confused, Socrates rejected these explanations, seeking a method of his own instead.
Then Socrates stumbled upon the teachings of Anaxagoras, who asserted that "intelligence" organizes all things, and thus is the reason for everything. This explanation pleased Socrates, and he reasoned further that "intelligence" would always organize things in the way that is best. Therefore, to discover the reason for anything's coming to be, ceasing to be, or continuing to be, one need only ask how it that thing should best be. Excited at this prospect, Socrates eagerly bought Anaxagoras' books, hoping to learn all sorts of things about the earth and the heavens, all explained in terms of how it is best that they should be.
However, Socrates fast grew disappointed with Anaxagoras. The reasons Anaxagoras adduced through his "intelligence" were purely physical explanations that did very little to convey a sense of order in the universe. For instance, an Anaxagorean account of why Socrates is presently sitting would consist in his bones, sinews, and muscles being a certain way and in a certain position, and an account of why he is speaking to his interlocutors would deal with sound and air and hearing. But none of Anaxagoras' theories would adduce the true reasons for Socrates' sitting and talking--that he was sentenced to death and thought it just to face the sentence rather than attempt an escape. After all, Socrates notes, his bones and sinews would be in a very different place right now had he judged it better to attempt an escape! Socrates' body being the way it is provides the conditions without which the reasons for his being here would not be possible, but the reasons themselves have more to do with Socrates' intelligence and his sense of what is best.
Socrates confesses that he would be delighted to learn the facts about the universe as Anaxagoras proposed, but to date he knows no one who can teach such causes. Instead, he has worked out for himself a secondary account of causation. Rather than deal directly with the facts, he formulates theories, and holds to the theory he considers most plausible. Then he takes as true whatever agrees with that theory, and as false whatever disagrees with it.
This section is concerned with the very difficult questions of causation: what reasons can we give for things being the way they are? And how can we know that they are the right reasons? We have three answers here, one from the natural sciences that Socrates studied, one from Anaxagoras, and one from Socrates himself. We are also presented with two different forms of explanation: material explanation and teleological explanation.
When Socrates refers to the natural sciences he studied, he is undoubtedly referring primarily to the teachings of Democritus and Empedocles. Democritus is famous for positing the existence of atoms, while Empedocles maintained that all matter is composed of the four basic elements: earth, air, fire, and water. Both men used these theories as material explanations for the workings of the universe. That is, their explanations explain how matter moves about in the universe and what forces cause change, somewhat similar to our present concepts of science. For these natural philosophers, things behave in accordance with necessity and chance. By necessity, materials behave in a certain way: for instance, earth always falls, fire rises, water is moist, etc. Sometimes, by chance, two materials will come together and combine, and depending on their relative proportions, they will form different compound substances, such as blood or bone. However, all these explanations only fix the laws governing the behavior of materials, and do not lay out any sort of reason for why they behave as they do. As Socrates notes, they are unable to give an account of complex organisms such as human beings.
Socrates is drawn to Anaxagoras, who seems to provide a teleological explanation rather than simply a material one. Teleological explanation does not exclude material explanation, but rather adds something to it, providing an account that relies on the end goal of an object. Thus, a teleological explanation might take into account the principle that fire rises and then provide a reason for it, explaining why rising should be the end goal of fire. Anaxagoras seems to provide this teleological explanation in the form of his "intelligence." According to his theory, the matter in the universe is all organized in accordance with "intelligence," which remains distinct from the material elements, and places things where they best belong. Much to Socrates' (or rather Plato's) disappointment, however, Anaxagoras does not give any account as to why "intelligence" deems the way things are to be the best possible way. Ultimately, Anaxagoras' explanation is essentially a material explanation, backed by an assertion that "intelligence" approves of this arrangement.
According to Socrates, causation cannot possibly be explained in terms of material explanation. A material cause (for instance, that Socrates is in his cell results from the way his body is situated) only provides those conditions without which the real cause could not operate. The real cause, then, is given by a teleological explanation. A teleological explanation will tell us why things are the way they are rather than simply explaining that they are the way they are. To get a grasp on such an explanation, Socrates turns to theory to solve his problems. His answer to what provides a teleological explanation for things, the Theory of Forms, will be detailed in the next section.