Plato, Theaetetus 191a

Soc. “For the sake of argument, imagine that there is a single chunk of wax in our minds, for some it is bigger, for some smaller, and for one the wax is clearer, while for another it is more contaminated and rather inflexible;  for others, in turn, the wax more pliable and even.”

Th. Ok….

Soc. Let us say that this is the gift of the Muses’ mother, Mnemosunê, and when we wish to recall something we have seen or heard or thought ourselves, we show this wax to our perceptions or thoughts and find the imprint, just as we find meaning in seal rings. Whatever is printed can be remembered and understood as long as its image persists. Whenever it is softened or cannot be recorded is forgotten and not understood.”

Soc. Θὲς δή μοι λόγου ἕνεκα ἐν ταῖς ψυχαῖς ἡμῶν ἐνὸν κήρινον ἐκμαγεῖον, τῷ μὲν μεῖζον, τῷ δ᾿ ἔλαττον, καὶ τῷ μὲν καθαρωτέρου κηροῦ, τῷ δὲ κοπρωδεστέρου, καὶ σκληροτέρου, ἐνίοις δὲ ὑγροτέρου, ἔστι δ᾿ οἷς μετρίως ἔχοντος.

ΘΕΑΙ.Τίθημι.

Soc. Δῶρον τοίνυν αὐτὸ φῶμεν εἶναι τῆς τῶν Μουσῶν μητρὸς Μνημοσύνης, καὶ ἐς τοῦτο, ὅ τι ἂν βουληθῶμεν μνημονεῦσαι ὧν ἂν ἴδωμεν ἢ ἀκούσωμεν ἢ αὐτοὶ ἐννοήσωμεν, ὑπέχοντας αὐτὸ ταῖς αἰσθήσεσι καὶ ἐννοίαις, ἀποτυποῦσθαι, ὥσπερ δακτυλίων σημεῖα ἐνσημαινομένους· καὶ ὃ μὲν ἂν ἐκμαγῇ, μνημονεύειν τε καὶ ἐπίστασθαι ἕως ἂν ἐνῇ τὸ εἴδωλον αὐτοῦ· ὃ δ᾿ ἂν ἐξαλειφθῇ ἢ μὴ οἷόν τε γένηται ἐκμαγῆναι, ἐπιλελῆσθαί τε καὶ μὴ ἐπίστασθαι.

Thanks to S. Raudnitz for drawing my attention to the passage from the Theaetetus

Quintilian’s Inst. Orat. 6.2

“The fictions I have been talking about pursue us when our minds are at rest as empty hopes or certain daydreams so that we imagine we are on a journey, sailing, fighting, talking to new people, or distributing wealth we do not have—and we seem not to be considering but to be doing these things. Couldn’t we transfer this vice of the mind to something useful?”

quod quidem nobis volentibus facile continget; nisi vero inter otia animorum et spes inanes et velut somnia quaedam vigilantium ita nos hae de quibus loquor imagines prosecuntur ut peregrinari navigare proeliari, populos adloqui, divitiarum quas non habemus usum videamur disponere, nec cogitare sed facere, hoc animi vitium ad utilitatem non transferemus [ad hominem]

I do believe that, along with Aristotle and Plato, Lavar Burton might disagree with Quintilian’s dismissal of fantasy: