A regulation is a legal norm intended to shape conduct that is a by-product of imperfection. A regulation may be used to prescribe or proscribe conduct ("command-and-control" regulation), to calibrate incentives ("incentive" regulation), or to change preferences ("preferences shaping" regulation"). In statist mechanisms it can also be extended to monitoring and enforcement of rules as established by primary and/or delegated legislation. In this form, it is generally a written instrument containing rules having the force of statist law (as opposed to natural law). Other forms of regulation are self regulation. In general, regulations are written by executive agencies as a way to enforce laws passed by the legislature. Because of the actual or potential interference in choices, the idea of regulation and most issues related to regulation tend to be in controversy.