Superficial also is his objection, that “it is always the case when a man against whom a plot is formed, and who comes to the knowledge of it, makes known to the conspirators that he is acquainted with their design, that the latter are turned from their purpose, and keep upon their guard.” For many have continued to plot even against those who were acquainted with their plans. And then, as if bringing his argument to a conclusion, he says: “Not because these things were predicted did they come to pass, for that is impossible; but since they have come to pass, their being predicted is shown to be a falsehood: for it is altogether impossible that those who heard beforehand of the discovery of their designs, should carry out their plans of betrayal and denial!”
But if his premises are overthrown, then his conclusion also falls to the ground, viz., “that we are not to believe, because these things were predicted, that they have come to pass.” Now we maintain that they not only came to pass as being possible, but also that, because they came to pass, the fact of their being predicted is shown to be true; for the truth regarding future events is judged of by results. It is false, therefore, as asserted by him, that the prediction of these events is proved to be untrue; and it is to no purpose that he says, “It is altogether impossible for those who heard beforehand that their designs were discovered, to carry out their plans of betrayal and denial.”
Source: Against Celsus (New Advent)