To produce intelligence objectively, the analyst must employ a process tailored to the nature of the problem. Four basic types of reasoning apply to intelligence analysis: induction, deduction, abduction and the scientific method. The induction process is one of discovering relationships among the phenomena under study. It may come from human pattern recognition ability, looking at a seemingly random set of events, perhaps writing them on cards and shuffling them until a pattern emerges. An analyst might notice that when Country X's command post with call sign ABC sent out a message on frequency 1 between Thursday and Saturday, an air unit will move to a training range within one week. The acknowledgement will take one day, so the analyst should recommend intensified COMINT monitoring of the appropriate frequencies between Friday and Sunday. Another kind of causality could come from interviews, in which soldiers might describe the things that warn them of an impending attack, or how the ground might look when an improvised explosive device has been emplaced. While induction, for human beings, is usually not at a fully rational level, do not discount the potential role of software that uses statistical or logical techniques for finding patterns. Induction is subtly different from intuition: there usually is a pattern that induction recognizes, and this pattern may be applicable to other situations. Deduction, is the classic process of reasoning from the general to the specific, a process made memorable by Sherlock Holmes: "How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?" Deduction can be used to validate a hypothesis by working from premises to conclusion. The pattern of air maneuvers described above may be a general pattern, or it may be purely General X's personal command style. Analysts need to look at variables, such as personalities, to learn whether a pattern is truly general doctrine, or simply idiosyncratic. Not all intelligence officers regard this as a desirable approach. At his confirmation hearing for CIA Director, Gen. Michael V. Hayden said he believes that intelligence analysis should be done by "induction", under which "all the data" are gathered and general conclusions determined, rather than by "deduction", under which you have a conclusion and seek out the data that support it. Analysts need to harness trained intuition: the recognition that one has come to a spontaneous insight. The steps leading there may not be apparent, although it is well to validate the intuition with the facts and tools that are available. Polish cryptanalysts first were reading German Enigma ciphers in 1932, although the commercial version may have been broken by the British cryptanalyst, Dilwyn Knox, in the 1920s.