Quis custodiet ipsos custodes? is a Latin phrase found in the work of the Roman poet Juvenal from his Satires (Satire VI, lines 347–348). It is literally translated as “Who will guard the guards themselves?“, though it is also known by variant translations, such as “Who watches the watchers?” and “Who will watch the watchmen?“.
This phrase is used generally to consider the embodiment of the philosophical question as to how power can be held to account. It is sometimes incorrectly attributed as a direct quotation from Plato‘s Republic in both popular media and academic contexts. There is no exact parallel in the Republic, but it is used by modern authors to express Socrates‘ concerns about the guardians, the solution to which is to properly train their souls.
Several 19th-century examples of the association with Plato can be found, often dropping “ipsos”. John Stuart Mill quotes it thus in Considerations on Representative Government (1861), though without reference to Plato. Plato’s Republic though was hardly ever referenced by classical Latin authors like Juvenal, and it has been noted that it simply disappeared from literary awareness for a thousand years except for traces in the writings of Cicero and St. Augustine. In the Republic, a putatively perfect society is described by Socrates, the main character in this Socratic dialogue.
Socrates proposed a guardian class to protect that society, and the custodes (watchmen) from the Satires are often interpreted as being parallel to the Platonic guardians (phylakes in Greek). Socrates’ answer to the problem is, in essence, that the guardians will be manipulated to guard themselves against themselves via a deception often called the “noble lie” in English. As Leonid Hurwicz pointed out in his 2007 lecture on accepting the Nobel Memorial Prize in Economic Sciences, one of Socrates’ interlocutors in the Republic, Glaucon, even goes so far as to say “it would be absurd that a guardian should need a guard.”