I am trying to think of what the name of the word/phrase is for when:

An important task (not a difficult one, but a mission critical one) is at hand and instead of one person being assigned to it, a group takes on the responsibility to mitigate any consequences happening to one person in case something goes wrong and also to prevent a mistake or malicious intent occurring from one persons doing. (NOT because the task is big and needs to be divided in a group.)


  1. Two different people needing to turn a key each in a device simultaneously to launch a missile.

  2. Group of people tallying up votes for an election in case one of them were bridged to rig the outcome.

  • In addition to Edwin's comprehensive answer, I would mention a phrase that appears in the Wikipedia article he cites (which I have heard in real life): "two-person integrity" (TPI).  While it doesn't use that specific phrase, this comment suggests that two trusted Apple employees would need cooperate to handle the security-related aspect of producing the unlocking software that the FBI is asking them to write. Commented Mar 20, 2016 at 21:02
  • I would have said distribute responsibility after reading your text, not divide. Ashworth answer is correct.
    – user116032
    Commented Mar 20, 2016 at 23:16

1 Answer 1


In the US, and not just for the case where two persons are involved, this is known rather predictably as the two-man rule.

From Wikipedia:

[The examples and perspective in this article deal primarily with the United States and do not represent a worldwide view of the subject.]

The two-man rule is a control mechanism designed to achieve a high level of security for especially critical material or operations. Under this rule all access and actions requires the presence of two authorized people at all times.

Nuclear weapons

Per US Air Force Instruction (AFI) 91-104, "The Two-Person Concept" is designed to prevent accidental or malicious launch of nuclear weapons by a single individual....

No-lone zone

A no-lone zone is an area that must be staffed by two or more qualified or cleared individuals. Each individual must be within visual contact with each other and in visual contact with the critical component that requires a no-lone-zone area designation. A no-lone zone may contain a cryptographic component, weapon system hardware under test, a nuclear weapon or active nuclear weapon controls....

Other uses

The two-man rule is used in other safety critical applications where the presence of two people is required before a potentially hazardous operation can be performed. This is common safety practice in, for example, laboratories and machine shops. In such a context, the additional security may be less important than the fact that if one individual is injured the other can call for help. As another example, firefighters operating in a hazardous environment (i.e. interior structure fire, HAZMAT zone, also known as IDLH, or Immediately Dangerous to Life or Health) function as a team of at least 2 or more personnel. There are commonly more than one team in the same environment, but each team operates as a unit.

Dual keys require the authorization of two separate parties before a particular action is taken. The simplest form of dual key security is a lock that requires two keys to unlock it. The two keys would be in the possession of two separate persons. The lock could only be opened if both parties agreed to open it and at the same time. In 1963, Canada accepted having American W-40 nuclear warheads under dual key control on Canadian soil, to be used on the Canadian BOMARC missiles.

In business, the four-eye principle means that "all business decisions and transactions need approval from the CEO and CFO. Since the CFO is not reporting to the CEO, there is an independent controlling mechanism in place"....

Civilian aircraft

In late March 2015 many national aviation authorities and/or airlines made the cockpits of aircraft in flight mandatory "two-man" or "no-lone zones" as a result of the Germanwings Flight 9525 crash. Early on in the investigation of that crash, it was believed from the cockpit voice recorder audio, and later supported by flight data recorder information, that the co-pilot deliberately crashed the aircraft after locking the cockpit door when the chief pilot left to use the toilet....

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.