Of course someone might stumble on the same sentence by chance, so, realistically, it might be difficult to prove that someone has plagiarized if they copied only a single sentence. But once someone has copied several consecutive sentences, the case is closed. Merely changing a few words is still plagiarism. The problem, in its most general form, is this. But as parents, we do play favorites.
Parental love is partial through and through.
Therefore, it would seem, one or the other of these conceptions has to be modified or abandoned. Nonetheless, we parents do play favorites. Parental love is completely partial. We think this is morally acceptable. In fact, we think there is something objectionable about the parent who is not partial toward his own children.