Course Hero. "Dialogues of Plato Study Guide." Course Hero. 13 Oct. 2017. Web. 22 July 2018. <https://www.coursehero.com/lit/Dialogues-of-Plato/>.
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Course Hero. "Dialogues of Plato Study Guide." October 13, 2017. Accessed July 22, 2018. https://www.coursehero.com/lit/Dialogues-of-Plato/.
Course Hero, "Dialogues of Plato Study Guide," October 13, 2017, accessed July 22, 2018, https://www.coursehero.com/lit/Dialogues-of-Plato/.
Socrates asks for definitions of ethical concepts, such as "What is justice?" "What is piety?" and "What is courage?" Generically, these are often thought of as "What is X?" questions. A major feature of Socrates's question is that the answer must be exclusive (i.e., that X is Y and nothing else is Y, or at least the portion of Y that is X must be labeled exclusively as such). It is the genus under which the species are classed, as, for example, the genus dog includes German shepherd, pit bull, Labrador retriever, and so forth.
The dialogues provide additional ways to think about the requirements for a good answer to a "What is X?" question. For example, the definition provides a common nature, a common idea under which particulars are united; that is, "its essential nature." The definition provides that which is the same in a group of particulars. Thus, in the Meno, we see that "figure" is included in any particular thing with color.
Whatever X is, it is real. The question has an answer that can be known; a definition that can be explicated. It is not, however, the dictionary sort of definition. The word is used in everyday life, yet its definition seems to be unknown to all.
The forms make possible everything that is. Socrates does not present the forms as the answer to the "What is X?" questions, but Plato does. They meet all the criteria for a good definition, thereby providing the answer Socrates seeks. What Plato's forms do for ethical concepts, they do for any and every individual thing: they make that thing possible.
The forms are eternal, immaterial, and unchangeable. They are the cause of what there is, even if Plato is not entirely clear how that causation occurs. Another way to think about the forms is in terms of individual things' dependency on them. Just as a shadow is dependent on the object that casts it, an individual object is dependent on its form.