Which definition best fits theft?

The definition of theft that best fits the legal framework is the unlawful appropriation with intent to permanently deprive. This definition encapsulates the essential elements required to establish the crime of theft under relevant laws, such as the Theft Act 1968 in England and Wales.

The term "unlawful appropriation" indicates that the act of taking property is done without the owner's consent, which is a critical aspect of theft. The addition of "with intent to permanently deprive" signifies that the thief not only takes the property but also does so with the intention of keeping it, thereby denying the owner the rights to their property irreversibly. Thus, both components are necessary to meet the legal definition of theft, emphasizing the criminality of the act and the conscious decision to deprive the rightful owner of their belongings permanently.

The other options do not meet the legal standards for theft. For instance, taking property with permission does not constitute theft, as consent negates the unlawful element. Temporary borrowing without intention to return lacks the requisite intent to permanently deprive, and misunderstanding ownership does not involve the intention to steal, making it inadequate for defining theft.