Theft is a general term embracing a wide variety of misconduct by which a person is improperly deprived of his property. The purpose of theft law is to promote security of property by threatening aggressors with punishment. Property security is valued as part of the individual's enjoyment of his belongings and because the community wishes to encourage saving and economic planning, which would be jeopardized if accumulated property could be plundered with impunity. Another function of the law of theft is to divert the powerful acquisitive instinct from non-productive preying on others to productive activity.
One problem that dogs the law of theft, as will be seen below, is that in a commercial society no clear line can be drawn between greedy antisocial acquisitive behavior on the one hand and, on the other hand, aggressive selling, advertising, and other entrepreneurial activity that is highly regarded or at least commonly tolerated. Here two important principles of constitutional and criminal law come into play to restrict the scope of the law of theft. A criminal law must not be so comprehensive as to jeopardize the ordinary behavior of decent citizens. Nor may a criminal law be so vague that it fails to warn the citizen what is forbidden and leaves to the discretion of enforcement officers or judges whether certain behavior should be punishable. The tension between these principles, and the impulse to penalize all egregious greed, account for the fact that theft law inevitably falls short of penalizing all rascality. At the same time—such are the refractory problems of legislative drafting—it is impossible, even with the most painstaking draftsmanship, to avoid overpenalizing in some cases. For example, obviously trivial peculations such as using an employer's stationery for writing personal notes quite clearly fall within theft law; yet it has proved impossible to articulate exceptions that will exclude this and a myriad of other trivial violations. Such things remain, therefore, within the province of prosecutorial and judicial discretion.
Within the broad category of theft, the law has long made important distinctions according to the particular means employed to appropriate the property, the nature and value of the property, the "criminal intent" or its absence, and other circumstances. These variables are reflected in the number of distinct criminal offenses that the law developed to deal with theft—for example, larceny, embezzlement, false pretense, fraudulent conversion, cheating, robbery, extortion, shoplifting, and receiving stolen goods. Before the emergence of the British Parliament and royal courts as the dominant lawmaking institutions, it may be assumed that all such misbehavior was subject to the rather arbitrary sanctions of local baronial justice.
A uniform central justice would first be invoked in the most serious cases, especially where capital punishment might be imposed. Thus, the great "common law felonies"–treason, murder, arson, rape, robbery, and burglary—became the first concern. Of these, robbery and burglary were typically property crimes, but with distinctive circumstances of aggravation. Robbery with theft accompanied by personal violence was notably an offense of the highway, impairing the security of a communications network that was important to the monarchy and to commercial interests. Burglary involved violent invasion of the home for felonious purpose (not necessarily theft) at night. One may speculate that burglary was an early concern of royal courts because it, like arson, occurred as an incident of warfare among the barons or of peasant revolts. As time passed, the aggravating circumstances sufficing for royal jurisdiction of these felonies were attenuated. By the end of the eighteenth century, a purse-snatching in London would be robbery in view of the "violence" suffered by the owner from the momentary pull of the purse handle. A thief became a burglar if he opened the door of a henhouse on the home lot of a townsman.