Following a review of the historical emergence of the categorical concept of probable cause against unknown persons, the ethical implications of investigating individuals based solely upon their categorical membership is analyzed. The moral wrong that may be inflicted upon individuals by judging them in terms of statistical characteristics may include stigmatization that results in limited educational and economic opportunites, differential probability and severity of criminal punishment, and psychological stress. Although the examples presented by Braithwaite et al concerning the targets to be selected for covert facilitation suggest that probable cause requires sufficient evidentiary bases for tempting certain individuals, such an approach usually will be unworkable because of difficulty in collecting the necessary evidence. Given this, random or equal probability selection of known targets within a category could provide a fair principle for target selection. In addition, legislative evidentiary standards of categorical probable cause could also contribute to more democratic policing. 9 references.