Anaxagoras - the mind causes all things

In the Phaedo, Socrates says ....

• “Then one day I heard a man reading from a book, as he said, by Anaxagoras, [97c] that it is the mind that arranges and causes all things. I was pleased with this theory of cause, and it seemed to me to be somehow right that the mind should be the cause of all things, and I thought, 'If this is so, the mind in arranging things arranges everything and establishes each thing as it is best for it to be'. 
• So if anyone wishes to find the cause of the generation or destruction or existence of a particular thing, he must find out what sort of existence, or passive state of any kind, or activity is best for it."
•  Plato, Phaedo, section 97c
• As I considered these things I was delighted to think that I had found in Anaxagoras a teacher of the cause of things
•   Plato, Phaedo, section 97d 
• [98b] So I thought when he assigned the cause of each thing and of all things in common he would go on and explain what is best for each and what is good for all in common.
•   Plato, Phaedo, section 98b

in: Plato in Twelve Volumes, Vol. 1 translated by Harold North Fowler; Introduction by W.R.M. Lamb. Cambridge, MA, Harvard University Press; London, William Heinemann Ltd. 1966. 1925

Plato - Unwritten Doctrines

Giovanni Reale wrote in his History of Ancient Philosophy (1992):

• ... the writings have not been for Plato the full expression or the most important communication of his thought, and therefore the reading and the interpretation of the dialogues are to be reassessed through a new vision. (p. 8)
• We are hence able ... to understand why so great a writer could be convinced of the limited character of the communicative function of writing; and therefore we are finally in a position to interpret his self-testimony contained in the Phaedrus in a correct manner .. (p. 9)
• ... Aristotle himself has told us that these teachings that Plato communicated only in oral discussions were called the Unwritten Doctrines (aàgrafa dógmata). (p. 14)

Reale, Giovanni (1990) A History of ancient philosophy. Vol.2 Plato and Aristotle. Translation of: Storia della filosofia antica, 5th edition. Edited and translated  by John R. Catan. Albany (NY): State University of New York Press.