What legal principle is applied when using or loaning out a chattel without permission, resulting in damage that affects its value?

The principle at play when a chattel is used or loaned out without permission, resulting in damage that affects its value, is known as conversion. Conversion involves the unauthorized taking or control of someone else's property, which deprives the owner of their rights to that property. In this scenario, the act of using or loaning the chattel without the owner's consent means that the person is exercising control over the property in a manner that violates the owner's rights, potentially leading to its damage and a loss in value.

This principle captures not just the physical act of taking or borrowing the item but also the implications of that act upon the owner's property rights. The focus of conversion is on the wrongful interference with the owner's ability to enjoy their property. In contrast, negligence would involve a failure to act in a reasonable manner that results in harm, but would not necessarily encompass the unauthorized use aspect. Title transfer and possessory lien do not apply, as they relate to the ownership or rights of possession rather than the wrongful use leading to damage. Thus, conversion accurately reflects the legal principle in this situation.