Certain difficulties have arisen from the requirement of "reasonable grounds for suspicion" in stop and search. These should be seen as a by-product of specific factors in the legislative emergence of the Police and Criminal Evidence Act 1984 (PACE). One of the problems is the stereotyping of black youth as a group, leading to the extensive use of stop and search powers against them. This issue became an attempt to exclude stereotyping as an adequate ground for suspicion, but failed to take into account the "incongruity procedure," where individuals attract suspicion not because they accord to a stereotype, but because they fail to fit into variable contexts of activity, place, and time considered to be normal. This use of suspicion is highly valued in police culture. Another reason why the PACE power of stop and search fits uneasily with the practice of policework is that PACE treats stop and search as an event rather than as a social process. Suspicion is not just a preparatory stage of detection of a specific crime: it is also central to more general police duties of surveillance and crime prevention. Other problems are discussed. The rules at present governing stop and search have not achieved the stated objectives and have harmed the relationship between the police and sections of the public. 60 references.