… For much of American history, politicians viewed secrecy and spying with disdain; these practices seemed suited for Old World autocrats and royal-court conspirators, not for citizens of a democracy. As late as 1908, when Attorney General Charles Bonaparte appealed for funds to create a small bureau of investigation within the Justice Department, Congress met his proposal with cries of dismay. ‘‘If Anglo-Saxon civilization stands for anything,’’ the Kentucky representative Swagar Sherley declared, ‘‘it is for a government where the humblest citizen is safeguarded against the secret activities of the executive of the government.’’

Bonaparte went ahead and created his bureau anyway: the forerunner of today’s F.B.I. World War I gave that bureau a new raison d’être, transforming a small band of detectives into a modern intelligence operation, charged with investigating wartime loyalty under new laws like the 1917 Espionage Act. After World War II, a permanent classification system took hold. The Oxford English Dictionary identifies 1940 as the moment when ‘‘classified’’ began to mean ‘‘designated as officially secret; accessible or known only to authorized people.’’ Before that, to be a ‘‘classified’’ employee was simply to be a member of the Civil Service whose job could be sorted into some grade or rank.

Some of what was ‘‘classified’’ under the new system involved vital intelligence matters: military plans, weapons technology, the names of informants overseas. But government officials also claimed the right to conduct sensitive negotiations in confidence, and the system rapidly expanded to include routine bureaucratic business. This secrecy was a useful tool, but it became a crutch too — a way for federal employees to cover up mistakes or to inflate their own importance. ‘‘In a culture of secrecy,’’ the Moynihan Commission noted, ‘‘that which is not secret is easily disregarded or dismissed,’’ producing powerful incentives for government officials to classify pretty much everything. (And little incentive not to; why risk scrutiny?) Thus began the problem of overclassification, in which even humdrum exchanges end up labeled ‘‘Top Secret,’’ ‘‘Secret,’’ ‘‘Confidential’’ or at least ‘‘Restricted,’’ the four categories laid out by Harry Truman in his 1951 executive order establishing the modern classification system.

This could produce absurd results. In the 1950s, according to the historian Sam Lebovic, the Labor Department refused to say how much peanut butter the Army had purchased, for fear that enemy number-crunchers might figure out the size of the armed forces, a statistic that was already public….