Diotima shares with Socrates the process by which one can attain the final visions of the mysteries. One begins as a young boy by being attracted to beautiful bodies, and to one beautiful body in particular, and produce beautiful discourses with this body. The next stage is to recognize that all bodies are relatively similar and that it is foolish to love only one body in particular. Thus, the boy will come to love all beautiful bodies. Next, he will come to appreciate the beauty of minds, and will be able to love those who are beautiful in mind whether or not they are beautiful in body. Recognizing the beauty in practices and laws, he will come to see that all kinds of beauty are similar and come to love beauty in general rather than beauty of bodies in particular. Looking at the different forms of knowledge, he will become a lover of knowledge, loving all sorts of discourses and ideas until he finally settles on one special type of knowledge.
Ultimately, this lover of knowledge will reach the goal of love, which is amazingly beautiful in its nature. This beauty always exists, not coming into being or ceasing to be, nor increasing nor diminishing. It is absolute beauty, not being beautiful only in some respects or at some times or in relation to certain things or in certain places or to certain people. Beauty will not appear in certain bodies or in certain forms of knowledge or anywhere in particular: it will appear in itself and by itself, independent of everything else. All beautiful things share in its character, but these things in no way affect Beauty itself.
By going through these stages, one will ascend from loving particular kinds of beauty to loving Beauty itself, from which all beautiful things derive their nature. Diotima suggests that a life gazing upon and pursuing this Beauty is the best life one can lead. Many of us can give up all luxuries in order to gaze upon and be with someone we love. Imagine, then, she urges, what it would be like to gaze upon Beauty itself, which is so much greater than the beauty of boys, men, clothes, money, and all else that it is the source of the beauty of these lesser things. Such a person would be able also to produce true virtue rather than images of virtue. Those who are obsessed with images of beauty can only produce images of virtue, but those who can see Beauty itself can produce virtue itself, making themselves immortal and loved by the gods.
This is the end of Diotima's speech as transmitted through Socrates, and Socrates concludes that ever since speaking with Diotima he has known that there is no greater partner for human nature than Love. Socrates says that he has finished, though he is not sure if his speech counts as a eulogy of Love, or whatever one might call what he has just described.
This passage may seem very confusing to readers not familiar with Plato. But those who know his other middle-period dialogues, such as the Phaedo or the Republic, will recognize in Diotima's discussion of Beauty Plato's famous Theory of Forms, even though forms are not explicitly mentioned in this passage and the whole presentation is conducted in an opaque and ambiguous manner.
The Theory of Forms states that for every concept, such as justice, beauty, good, large, etc. (there is some debate as to what different kinds of Forms there are) there is a Form of that concept. That is, there is the Form of Justice, the Form of Beauty, the Form of Good, the Form of Large, and so on. These Forms are absolute, immortal, unchanging, and not admitting of their opposites (that is, the Form of Beauty cannot in any way admit of ugliness). All things that are, say, beautiful, are beautiful because they participate in the Form of Beauty. We can understand all beautiful things as sharing in the Form of Beauty, and it is only because of their participation in the Form of Beauty that they can be beautiful. The Form of Beauty, then, is that by means of which all beautiful things are beautiful. It is the essence of Beauty.
In the Symposium, the Form of Beauty is the final stage in the lover of knowledge's ascent toward Beauty. He begins by loving particular bodies, moving from there to bodies in general, to particular minds, to minds in general, to laws and practices, to knowledge, and finally to the knowledge of the Form of Beauty. The ascent is one of increasing generalization where one's love of beauty comes to embrace more and more things. Ultimately, however, one's love of beauty will embrace only one thing, the Form of Beauty, but one will recognize in this Form all that is beautiful.
There are a number of questions and debates about the correct interpretation of the Theory of Forms. For instance, we might ask what concepts have Forms and what don't. Is there a Form of Snow or a Form of Chair? We might also ask in what way particular things can participate in a Form: is it in the way that a drop of water is a part of the sea, is it that the Form represents what all the particulars share in common, is the Form a paradigm that the particulars aspire to, or is it something else entirely? These questions are beyond the scope of this commentary, though they are examined more closely in the commentary in the SparkNote on Plato's ##Phaedo##. We can also find a compelling and interesting self-criticism of the Theory of Forms in Plato's Parmenides.
Our knowledge of Forms seems to be quite distinct from our knowledge of everyday things, and there is some question as to how we can come to know Forms. Plato here presents this knowledge as the final destination of a long ascent. Significantly, though, it is not Socrates who gives us this answer, but rather Diotima. Diotima speaks through Socrates almost as an oracle, a source of truth. Socrates himself never claims such knowledge. This is particularly interesting if we read it in the wider context of Plato's works. The Theory of Forms is first introduced in the Phaedo, but there also we are given reason to suppose that Socrates is not speaking from himself but rather from some kind of divine inspiration. We might conclude that knowledge of Forms is not something that can be learned through the Socratic dialectic, but that it is, in some sense, a prophetic gift. At best, dialogue can lead us toward the Forms, but we need some other kind of inspiration to know the Forms directly.