The elements of larceny include (1) a trespassory (wrongful) (2) taking (3) and carrying away (4) of the personal property (5) of another person (6) with the intent to deprive the owner of the property permanently.
(1) A trespassory (wrongful) (2) taking...
Since larceny is a specific intent crime, the law requires considering whether there's an intent to steal or a genuine intent to return something.
...when property has been lost (Diamond, pp. 478-484)
At common law, the prosecution must prove an additional two elements when the property taken was first lost: (7) that, at the time the defendant took the property, the defendant had a clue suggesting that the owner could reasonably be found; and (8) that the defendant had the intent to permanently deprive the owner of the property at the time it was taken. The MPC eliminates both requirements and generally criminalizes all failures to return lost property.
...when property delivered by mistake (Diamond, pp. 486-489)
Again, at common law, two more elements are required in this situation: (7) knowledge by the defendant at the time of taking that the victim made a mistake as to the nature or the amount of the property or to whom it was delivered; and (8) that the defendant had the intent to permanently deprive the owner of the property at the time it was taken. Under the MPC, the time of forming the intent doesn't matter (§ 223.5).