The Associated Press Stylebook offers concrete guidance on anonymous source use. Surprisingly, the stylebook did not dedicate an entry on the subject until 2004. That year’s entry reads:

Use anonymous attribution only when essential and even then provide the most specific possible identification of the source. Simply quoting “a source,” unmodified, is almost always prohibited. Do not attribute information to sources – anonymous or otherwise – when it is obvious, common sense or well-known. The basic guidelines for use of anonymous sources: The material must not be available except under the conditions of anonymity imposed by the source. In some cases, it may be appropriate to say why the source requested anonymity. The source must be in a position to have accurate information, and, to the best of the reporter’s ability to determine, must be understood to be reliable. Be sure to seek more than one source for the story. (p. 17)

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The AP entry offers specific guidance on normative journalistic behavior. The entry suggests reporters only use anonymous attribution when “essential,” although it doesn’t offer any criteria for determining such a condition. The entry prohibits the anonymous attribution of “common sense” information, although few critics complained that such reporting was part of the problem. The entry is also riddled with room for journalistic rationalization. Reporters should “almost always” avoid anonymous attribution without any description of the source’s identity. Journalists should “seek” a second source, but the entry doesn’t prohibit reporting if the journalist can’t find one. The book offers normative guidelines, but they don’t seem strict enough to affect the decision-making process.

The 2009 Associated Press Stylebook revised the entry substantially with changes removing some of the wiggle room from the previous entry, although in one case the standards were loosened. It reads:

Whenever possible, we pursue information on the record. When a source insists on background of off-the-record ground rules, we must adhere to a strict set of guidelines. Under AP’s rules material from anonymous sources may be used only if: [a] The material is information and is not opinion or speculation, and is vital to the news report. [b] The information is not available except under the conditions of anonymity imposed by the source. [c] The source is reliable, and in a position to have accurate information. Reporters who intend to use material from anonymous sources must get approval from their news managers. Explain in the story why the sources requested anonymity. And, when it’s relevant, describe the source’s motive for disclosing the information. The story also must provide attribution that establishes the source’s credibility; simply quoting “a source” is not allowed. Be as descriptive as possible.

In a tightening of protocol, reporters are now told they must explain why the source requested anonymity instead of reserving that action for “some cases.” Journalists are also instructed to consider disclosing the motive for the source’s actions, a recommendation left out of the 2004 version. Reporters must now always provide a description of the source to help with credibility not just in some cases. And reporters must also seek the approval of their boss to use anonymous information.

These changes represent palpable, inflexible restrictions on anonymous source use. However, in one important respect, the AP loosened the rules. The suggestion to seek a second source has been removed entirely. The journalistic tradition of verifying anonymous information is no longer required by the Associated Press.