(Kuno and Kaburaki 1977: 645) The two sentences in (19) and (20) fundamentally deliver identical situations in their logical content, but they seem to differ from each other in the standpoint from which the speaker has intentionally chosen to describe the events, and empathize more with a specific person.
it can be easily presupposed that the speaker empathizes more with John than with Mary in (19), while the speaker empathizes more with Mary than with John in (20).