Any unauthorized act that deprives an owner of personal property without his or her consent.
The wrongdoer converts the goods to his or her own use and excludes the owner from use and enjoyment of them. The English COMMON LAW early recognized such an act as wrongful and, by the middle of the fifteenth century, allowed an action in TROVER to compensate the aggrieved owner.
The earliest cases allowing a lawsuit for conversion were based on claims that the plaintiff had possession of certain items of PERSONAL PROPERTY, then casually lost them, and the defendant had found them and had not returned them but instead "converted them to his own use." This phrase was picked up, and it gave a name to a TORT that originally was a kind of ACTION ON THE CASE, a form of TRESPASS. As time passed, the plea that the plaintiff had lost his or her goods and the defendant had found them came to be considered a legal fiction (that is, a decision was made in the case as if the plea were true, and it did not have to be proved). The defendant was not allowed to dispute the allegations but could answer only the claim that the plaintiff had a right to possession of the goods and the defendant had refused to restore them to the plaintiff.
Today the word conversion is still applied to the unlawful taking or use of someone else's property. The type of property that can be converted is determined by the original nature of the CAUSE OF ACTION. It must be personal property, because real property cannot be lost and then found. It must be tangible, such as money, an animal, furniture, tools, or receipts. Crops or timber can be subject to conversion after they are severed from the ground. The rights in a paper—such as a life insurance policy, a stock certificate, or a promissory note—can be converted by one who appropriates the paper itself.
A thief, a trespasser, or a bailee may be guilty of conversion because the action may be maintained whether or not the property was lawfully acquired at the outset. For example, a dry cleaner who mistakenly delivers a suit to the wrong customer has converted it. Moving some-one's property without his or her permission might constitute a conversion if the inconvenience is substantial: for example, having some-one's car towed away in order to take the parking place. Unauthorized use is a conversion—such as a mechanic who, without permission, borrows a sports car that he or she is supposed to repair. Misuse of property can also be a conversion. If a neighbor lends his or her hedge trimmer to a friend, it is a conversion for the friend to use the hedge trimmer to cut down a tree.