The power of assumption. Marcus Aurelius 2.15

Some philosophers who inherited the mantle of Socrates did not believe that we could ever discover any uniform truth capable of resisting the corrosion of political consensus. Marcus thought they had a point. <Greek>.

Ὅτι πᾶν ὑπόληψις. δῆλα μὲν γὰρ τὰ πρὸς τὸν Κυνικὸν Μόνιμον λεγόμενα· δῆλον δὲ καὶ τὸ χρήσιμον τοῦ λεγομένου, ἐάν τις αὐτοῦ τὸ νόστιμον μέχρι τοῦ ἀληθοῦς δέχηται.

"Everything is assumption." These words attributed to the Cynic Monimus are clear (†). Their practical application is also evident, if one grasps the kernel of truth that they contain.

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(†) Monimus of Syracuse (4th century BCE) was a slave so impressed with reports of Diogenes of Sinope that he feigned gross incompetence to secure dismissal from the position he held in the household of his master, a Corinthian banker. Once freed from employment at the bank, he became a pupil of Diogenes. He also spent time with another famous Cynic, Crates of Thebes, whose abject poverty made it easier for Monimus' master to think him mad (Diogenes Laertius 6.82). 

The poet Menander credits Monimus with an aphorism essentially the same as that quoted by Marcus: "Everything is an illusion that we assume" (τὸ γὰρ ὑποληφθὲν τῦφον εἶναι πᾶν ἔφη, as recorded by Diogenes Laertius, 6.83). Given the wording of Marcus' attribution, which has the aphorism spoken to Monimus (πρὸς), it is possible to read it as something Monimus utters to articulate the response of the universe to his constant begging (προσαιτῶν) for truth. The seemingly fruitless outcome of his inquiry might remind some readers that the Cynics traced their philosophical lineage back to Socrates. Here is the passage from Menander:

         Μόνιμός τις ἦν ἄνθρωπος, ὦ Φίλων, σοφός,

         ἀδοξότερος μικρῷ δ’. Β. ὁ τὴν πήραν ἔχων;

         Α. πήρας μὲν οὖν τρεῖς· ἀλλ’ ἐκεῖνος ῥῆμά τι

         ἐφθέγξατ’ οὐδὲν ἐμφερές, μὰ τὸν Δία,

         τῷ γνῶθι σαυτόν, οὐδὲ τοῖς βοωμένοις

         τούτοις, ὑπὲρ δὲ ταῦθ’ ὁ προσαιτῶν καὶ ῥυπῶν·

         τὸ γὰρ ὑποληφθὲν τῦφον εἶναι πᾶν ἔφη.

         Monimus, Philon, was a sage

         Too little known in his own age.

         Had he a bag then? Oh, he did!
        Three, in fact! But naught he said.

         Other sages scream, by Zeus

         "Know thyself!" Their tongues are loose.

         Monimus these bleaters beat

         Begging ever in the street.

         Finally, one line he spoke:

         "All the world is human smoke!"

Sextus Empiricus also mentions Monimus, naming him alongside Metrodorus, Anaxarchus, and "others not a few" (οὐκ ὀλίγοι) as denying that there is any criterion of truth, which thereby becomes purely notional and consensual—a human fantasy without any sure footing beyond us (Adversus mathematicos 7.88).