τὸ γὰρ αὐτὸ νοεῖν ἐστίν τε καὶ εἶναι.

-- Parmenides

The usual translation of this fragment is “It is the same thing that can be thought and can be.” Yet, the literal Greek is more stunning: “To think and to be is the same thing.” This straightforward translation suggests that ‘being’ and ‘thinking’ are but different ways of expressing what is actually one. Thus, “being’ is not reduced to thinking as it is in some forms of idealism. Parmenides does think of the phenomenal world as illusory and so it is as long as the phenomenal world is posited as existing independently. The phenomenal world as such does not exist. Parmenides is, however, able to provide a logos of the phenomenal world precisely because it itself expresses attributes of thought as that which is thought about. Thus, are we also able to give meaning to dreams. The error, however, is to separate thinking from what is thought about. Once we understand being and thinking as the same thing, the phenomenal world is no longer phenomenal at all –there is no separation between thinking and what is thought about. There is only thinking. There is only what is. We are compelled, it seems, to live in a kind of exile from truth.

ταὐτὸν τὸ εἶναι καὶ τὸ νοεῖν εἶναι

-- Plotinus: 3.8.8

The same difficulty with translation exists here. Are we to translate this "It is the same thing that can be thought and can be" or "to think and to be are the same thing." Elmer O'Brien in his translation gives the later, more straightforward translation and puts the words in quotations, apparently in reference to Parmenides, as there is nothing in the Greek text itself that would indicate a quotation:

Clearly, in The Intelligence, subject and object are one. This identity is more than a close association such as we find in the best souls because "it is the same thing to think and to be." In The Intelligence we no longer have upon one side the object of contemplation and on the other that which contemplates. Were that so we would need another principle where the difference no longer exists. In The Intelligence the two things are one. (O'Brien, The Essential Plotinus, p. 170)

It is as if Plotinus is offering a commentary on the Parmenidean fragment. Yet, Plotinus pushes beyond the identity of thought and being to The Good:

If The Intelligence were itself the Good, why should it need to see or even to act in any way? Though other things act only for and by the Good, The Good has no such necessity: there is nothing for it except itself. After one has pronounced this word "Good," one should ascribe nothing further to it because any addition, of whatever sort, will make it less than it really is. Not even thought should be attributed to it. To do that would be to introduce a difference and thus make it a duality of intellection and goodness. The Intelligence needs the Good; the Good needs not The Intelligence. Upon attaining it, The Intelligence becomes like the Good because it is formed and perfected by it: see its trace, its imprint on The Intelligence and you can conceive the Good. Seeing this trace in itself, The Intelligence knows desire. (O'Brien, .174)