Plato in Charmides 167A-169C raises doubts about the idea that temperance is knowledge of what one knows and does not know. He remains uncertain whether there can be know ledge of knowledge (episteme epistemes) because of doubts about the analogous case of vision. Vision cannot be vision of itself and not of colour. Presumably, such vision would have no content, if colour was not included in the content. Analogously, knowledge of knowledge would be contentless.
One solution, Aristotelian in spirit, to Plato ’s problem would be that, when we are aware of seeing, we perceive that we perceive colour. So colour is not excluded after all, in Plato ’s way, from the content of the self-awareness.[...]
Aristotle believes that a disembodied intellect thinks itself. But on one interpretation of what he means, he would avoid the difficulty of contentless thought. Self-thinking is postulated in DA 3.4, 430a2-4; Metaph. 12.7, 1072bl9-21 (see also DA 3.4, 429b9; Metaph. 12.9, 1074b38-1075a5). In the first two passages a reason is given (as the word ‘for’ indicates) why the self-thinking occurs, [...], disembodied intellect is identical with what it thinks. Its thought may have a rich intellectual content. The divine Intellect postulated by Aristotle may be thinking philosophical  propositions. But in doing so, it thinks itself, because the propositions it thinks are, in the way explained, identical with itself. Though this is not the only explanation of Aristotle ’s divine Intellect being a self-thinker, it is given as an explanation by Aristotle , by Alexander DA 86,14-23; by ‘Alexander’ in Metaph. 698,1-15; and by Philoponus On Aristotle on Intellect 20,90-21,93; 21,7-16, and is endorsed as true of divine Intellect by Plotinus 5.3  5 (42-8). The point is put in terms of Intellect thinking itself incidentally (kata sumbebekos, secundum accidens) by Alexander DA 86,14-23 and Philoponus On Aristotle On Intellect 21,7-11. Aristotle himself says it appears that scientific understanding, perception, opinion, and discursive thought are directed to themselves only as a side effect (en parergoi), Metaph. 12.9, 1074b35-6.
Plotinus emphasises, as regards the human intellect, that even though it too is self-thinking, nothing follows about our being aware of its thinking [...]. That takes a special effort and mostly we are unaware of its thinking.
The identity which Aristotle postulates between intellect and what it thinks is the restricted kind of identity which he also postulates between the act of thinking and what is thought. This is not definitional identity: ‘thinking’ and ‘being thought’ do not mean the same thing. Rather, it is numerical identity: if you are counting activities, the activity of thinking and the object of thought acting on the mind, should not be counted as two activities, but as one. This is merely one example of the general causal principle of Phys. 3.3 about the activity of agent and patient, there illustrated by the case of teaching and being taught. Although the expressions ‘teaching’ and ‘being taught’ do not mean the same, there is only one activity going on, just as the road from Thebes to Athens and the road from Athens to Thebes are only one road.