Quis custodiet ipsos custodes?
Quis custodiet ipsos custodes? is a Latin phrase traditionally attributed to the Roman poet Juvenal from his Satires (Satire VI, lines 347–8), which is literally translated as "Who will guard the guards themselves?" Also sometimes rendered as "Who watches the watchmen?", the phrase has other idiomatic translations and adaptations such as "Who will watch the watch-guards?" In modern usage, it is frequently associated with the political philosophy of Plato and the problem of political corruption, but the original source has no known connection to Plato or political theory. The original context deals rather with the problem of ensuring marital fidelity. It has also been questioned whether the text of this particular passage is authentically part of Juvenal's Satires or is a later addition to the manuscript.
Original Context 
The phrase, as it is normally quoted in Latin, comes from the Satires of Juvenal, the 1st/2nd century Roman satirist. Although in its modern usage the phrase has universal, timeless applications to concepts such as tyrannical governments, uncontrollably oppressive dictatorships, and police or judicial corruption and overreach, in context within Juvenal's poem it refers to the impossibility of enforcing moral behaviour on women when the enforcers (custodes) are corruptible (Satire 6.346–348):
audio quid ueteres olim moneatis amici,
"pone seram, cohibe." sed quis custodiet ipsos
custodes? cauta est et ab illis incipit uxor.
I hear always the admonishment of my friends:
"Bolt her in, constrain her!" But who will guard
the guardians? The wife plans ahead and begins with them.
However, modern editors regard these three lines as an interpolation inserted into the text. In 1899 an undergraduate student at Oxford, E.O. Winstedt, discovered a manuscript (now known as O, for Oxoniensis) containing 34 lines which some believe to have been omitted from other texts of Juvenal's poem. The debate on this manuscript is ongoing, but even if the poem is not by Juvenal, it is likely that it preserves the original context of the phrase. If so, the original context is as follows (O 29–33):
consilia et ueteres quaecumque monetis amici,
"pone seram, cohibes." sed quis custodiet ipsos
custodes? qui nunc lasciuae furta puellae
hac mercede silent crimen commune tacetur.
… I know
the plan that my friends always advise me to adopt:
"Bolt her in, constrain her!" But who can watch
the watchmen? They keep quiet about the girl's
secrets and get her as their payment; everyone hushes it up.
This quotation is often and incorrectly attributed to Plato's Republic. However, there is no phrase in the Republic which is parallel or directly synonymous to it. It is commonly cited with regard to the problem of how to ensure that persons entrusted to watch over the interests of the state do so faithfully. 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."
See also 
- E.O. Winstedt 1899, "A Bodleian MS of Juvenal", Classical Review 13: 201–205.
- Recently J.D. Sosin 2000, "Ausonius' Juvenal and the Winstedt fragment", Classical Philology 95.2: 199–206 has argued for an early date for the poem.
- E.g. Who Are The Watchmen?; T. Besley and J.A. Robinson, "Quis Custodiet Ipsos Custodes? Civilian Control over the Military," Journal of the European Economic Association v. 8, pp. 655–663, 2010; and an earlier version of the present article.
- Plato (2008) [c. 380 BC]. The Republic. Benjamin Jowett, transl; EBook produced by Sue Asscher and David Widger. Project Gutenberg. "How then may we devise one of those needful falsehoods of which we lately spoke — just one royal lie which may deceive the rulers, if that be possible, and at any rate the rest of the city?"
- Book III, XII, 403E, p. 264 (Greek) and p. 265 (English), in volume I, of Plato, The Republic (ΠΟΛΙΤΕΙΑ), with an English translation by Paul Shorey, London, William Heinemann Ltd.; New York: G. P. Putnam’s sons, 1930, as cited by Leonid Hurwicz,"But Who Will Guard the Guardians?," Nobel Prize Lecture, December 8, 2007, Accessed 4-27-2011.