“Returns” means that the loss is restored “by its recovery,” that is, by recovery from the illness. For example, he usurps a sheep, then it becomes ill and its milk production decreases. It then recovers, and its milk returns to its normal state. Is he liable for that loss or not? The author says: he is not liable, because the loss that occurred while it was in his possession has been restored, and it has returned to its original condition. But if it were assumed that he returned it while it was ill, he would be liable. After it has recovered, however, he is not liable, because it has returned to the condition it was in at the time of usurpation. This is why he said: “Nor for an illness whose effects are restored by recovery,” meaning recovery from the illness. It should be understood, however, that he is liable for all the milk he took, because a usurper is liable for benefits. The discussion here concerns liability for tangible property.

“If the loss is restored through teaching it a craft, he is liable for the loss. And if it learns or gains weight, so that its value increases, then forgets or becomes emaciated, so that its value decreases, he is liable for the increase, just as if it were restored by something of a different kind from the original. But if it is restored by something of the same kind, he is liable only for whichever of the two is greater.”

His statement, “If the loss is restored through teaching it a craft, he is liable for the loss,” means: if the loss is restored not through recovery from illness, but through teaching it a craft, he is liable for the loss, because its restoration here is not a restoration of the loss that occurred.

An example is where he usurps a slave, who then becomes ill and emaciated. His value will undoubtedly decrease, but the usurper teaches him a craft by which his value rises. Thus, if the slave had been worth ten thousand before becoming ill, then, after falling ill, was worth five thousand, and thereafter learned a craft so that he became worth ten thousand—thus returning to his original value—is the usurper liable for his loss in value? The answer is yes, because the usurper is liable for the loss, while the increase belongs to the owner. We therefore say: the slave, without knowledge of the craft, is worth half of what he was worth before his value decreased; so he must return the slave and half of his value. Whatever increase resulted from learning the craft belongs to the owner.

Likewise, if he usurps a slave who can write, and the slave forgets how to write, but then learns the craft of electrical machinery, for example, and the loss caused by forgetting how to write is offset