the essence is the whatness of something, and this is determined as the dominant look, ἰδέα. But how does Plato come to this characterization of the essentiality of the essence? Is it obvious?
Not in the least, although we have long ago accustomed ourselves to more or less thoughtless talk about the "Ideas." For if the essence is identified with what something is, with the whatness, then the essence characterizes what a being is as such. In the essence as whatness or what-it-is, there resides therefore a conception of the being with regard to its Being. A being is in Greek τὸ ὄν, and what universally determines a being as a being is the κοινόν, the being in its beingness [Seiendheit], the ὄν in its οὐσία. Because the Greeks conceive the essence as the whatness of something and interpret the latter as "Idea," therefore the essence means the same as the beingness of beings, οὐσία, and therefore" the οὐσία of the ὄν is the ἰδέα, and therefore we can and should translate οὐσία, which actually and only denotes beingness, with "essence." This, however, as the general opinion confirms, is not at all obvious, and above all not for us modern and contemporary thinkers.
The reason the Greeks understand essence as whatness is that they in general understand the Being of beings (οὐσία) as what is constant and in its constancy is always present, and as present shows itself, and as self-showing offers its look — in short, as look, as ἰδέα. Only on the basis of this understanding of Being as constant self-opening and self-showing presence is the interpretation of the beingness of beings—hence the interpretation of οὐσία—as ἰδέα possible and necessary.
b) The Greek understanding of the ἰδέα.
In order to ascertain the correct understanding, i.e., the Greek understanding, of the ἰδέα, we must emphasize once more: the ἰδέα—εἶδος—is the look something offers in its "what," the look something exhibits of itself. Why do we stress this?
An objection could immediately be made—especially on the basis of the usual modern modes of thinking—that the characterization of the whatness as ἰδέα precisely does not fulfill what we desired, namely a determination of the whatness in itself. For