[There are] no secret documents in the romantic sense of the words. On any important subject, there is no single document or even group of documents that contain "the secret." No spy could know enough to spot such a document if it existed, and no vacuum cleaner approach to espionage, even should it gather up two or three documents of the highest importance, would lead without all the analytical skills of the humanists to any valid conclusions. Documents do not speak: they do not declare that they are "the offbeat thoughts and recommendations of a highly-placed but erratic advisor," not a draft intended only for discussion, not a record of a decision rescinded orally the next day.
Research and analysis are at the core of intelligence . . . . [Most] `facts' are without meaning; someone must analyze even the most easily obtained data.
Cloak and Gown
'Intelligence' refers to both a skill and end-product. As a meaningful concept it has been spoilt by Fleming, le Carre, and many other less talented writers. In the present context I would define it as the method employed by Sherlock Holmes; not the sleuth on the trail with his magnifying glass, but the intellectual sitting quietly and consuming his ounce of shag. It means reviewing known facts, sorting out significant from insignificant, assessing them severally and jointly, and arriving at a conclusion by the exercise of judgment: part induction, part deduction. Absolute intellectual honestly is essential. The process must not be muddied by emotion or prejudice, nor by a desire to please. The skill is largely innate, but can be sharpened by a course of rigorous academic training. The Americans talk about 'intelligence analysis' and 'analysts' and the terminology is crossing the Atlantic. It is not ideal, since the process is as much synthesis as analysis.
"Life in and out of Hut 3"
Code Breakers: The Inside Story of Bletchley Park
There is no such thing as the golden secret, the piece of 'pure intelligence', which will resolve all doubt and guide a general or admiral to an infallible solution of his operational problems. Not only is all intelligence less than completely accurate; its value is altered by the unrolling of events.
Intelligence in War