In many of his dialogues, Plato mentions supra-sensible entities he calls "Forms" (or "Ideas"). So, for example, in the Phaedo, we are told that particular sensible equal things—for example, equal sticks or stones (see Phaedo 74a-75d)—are equal because of their "participation" or "sharing" in the character of the Form of Equality, which is absolutely, changelessly, perfectly, and essentially equal. Plato sometimes characterizes this participation in the Form as a kind of imaging, or approximation of the Form. The same may be said of the many things that are greater or smaller and the Forms of Great and Small (Phaedo 75c-d), or the many tall things and the Form of Tall (Phaedo 100e), or the many beautiful things and the Form of Beauty (Phaedo 75c-d, Symposium 211e, Republic V.476c). When Plato writes about instances of Forms "approximating" Forms, it is easy to infer that, for Plato, Forms are exemplars. If so, Plato believes that The Form of Beauty is perfect beauty, the Form of Justice is perfect justice, and so forth. Conceiving of Forms in this way was important to Plato because it enabled the philosopher who grasps the entities to be best able to judge to what extent sensible instances of the Forms are good examples of the Forms they approximate.
Scholars disagree about the scope of what is often called "the theory of Forms," and question whether Plato began holding that there are only Forms for a small range of properties, such as tallness, equality, justice, beauty, and so on, and then widened the scope to include Forms corresponding to every term that can be applied to a multiplicity of instances. In the Republic, he writes as if there may be a great multiplicity of Forms—for example, in Book X of that work, we find him writing about the Form of Bed (see Republic X.596b). He may have come to believe that for any set of things that shares some property, there is a Form that gives unity to the set of things (and univocity to the term by which we refer to members of that set of things). Knowledge involves the recognition of the Forms (Republic V.475e-480a), and any reliable application of this knowledge will involve the ability compare the particular sensible instantiations of a property to the Form.
Immortality and Reincarnation
In the early transitional dialogue, the Meno, Plato has Socrates introduce the Orphic and Pythagorean idea that souls are immortal and existed before our births. All knowledge, he explains, is actually recollected from this prior existence. In perhaps the most famous passage in this dialogue, Socrates elicits recollection about geometry from one of Meno's slaves (Meno 81a-86b). Socrates' apparent interest in, and fairly sophisticated knowledge of, mathematics appears wholly new in this dialogue. It is an interest, however, that shows up plainly in the middle period dialogues, especially in the middle books of the Republic.
Several arguments for the immortality of the soul, and the idea that souls are reincarnated into different life forms, are also featured in Plato's Phaedo (which also includes the famous scene in which Socrates drinks the hemlock and utters his last words). Stylometry has tended to count the Phaedo among the early dialogues, whereas analysis of philosophical content has tended to place it at the beginning of the middle period. Similar accounts of the transmigration of souls may be found, with somewhat different details, in Book X of the Republic and in the Phaedrus, as well as in several dialogues of the late period, including the Timaeus and the Laws. No traces of the doctrine of recollection, or the theory of reincarnation or transmigration of souls, are to be found in the dialogues we listed above as those of the early period.
Metaxy (Greek: μεταξύ) or metaxu is defined in Plato's Symposium via the character of the priestess Diotima as the "in-between" or "middle ground". Diotima, tutoring Socrates, uses the term to show how oral tradition can be perceived by different people in different ways. In the poem by Socrates she depicts Eros as not an extreme or purity; rather, as a daimon Eros is in-between the divine Gods and mankind. Diotima thus exposes the flaws of oral tradition; it uses strong contrasts to express truth, thus revealing vulnerability to sophistry. This portion of the dialogue points to the idea that reality is perceptible only through one's character (which includes one's desires and prejudices and one's limited understanding of logic). Man moves through the world of Becoming, the ever changing world of sensory perception, into the world of Being—the world of forms, absolutes and transcendence, by Metaxy. Man transcends his place in Becoming by Eros, where man reaches the Highest Good, an intuitive and mystical state of consciousness. Neoplatonists like Plotinus later used the concept to express an ontological placement of Man between the Gods and animals. Much like Diotima did in expressing that Eros as daemon was in-between the Gods and mankind. Love (Ἔρως Eros) as the thing in between or child of Poverty (Πενία Penia) and Possession (Πόρος Poros)