First of all I wish to warn you that in disputations with unbelievers about articles of the Faith, you should not try to prove the Faith by necessary reasons. This would belittle the sublimity of the Faith, whose truth exceeds not only human minds but also those of angels; we believe in them only because they are revealed by God.
Yet whatever come from the Supreme Truth cannot be false, and what is not false cannot be repudiated by any necessary reason. Just as our Faith cannot be proved by necessary reasons, because it exceeds the human mind, so because of its truth it cannot be refuted by any necessary reason. So any Christian disputing about the articles of the Faith should not try to prove the Faith, but defend the Faith. Thus blessed Peter (1 Pet 3:15) did not say: “Always have your proof”, but “your answer ready,” so that reason can show that what the Catholic Faith holds is not false.