Thomas Aquinas Commentary Jeremiah 28:5-9

"Then the prophet Jeremiah said unto the prophet Hananiah in the presence of the priests, and in the presence of all the people that stood in the house of Jehovah, even the prophet Jeremiah said, Amen: Jehovah do so; Jehovah perform thy words which thou hast prophesied, to bring again the vessels of Jehovah`s house, and all them of the captivity, from Babylon unto this place. Nevertheless hear thou now this word that I speak in thine ears, and in the ears of all the people: The prophets that have been before me and before thee of old prophesied against many countries, and against great kingdoms, of war, and of evil, and of pestilence. The prophet that prophesieth of peace, when the word of the prophet shall come to pass, then shall the prophet be known, that Jehovah hath truly sent him." — Jeremiah 28:5-9 (ASV)

1. Here, Jeremiah’s response is given. First, he shows his emotion by desiring that what he had said would be fulfilled: amen, that is, “let it be.” It is as if he is saying, “If only I were not a man who has the Spirit, and was instead speaking a lie” . Jeremiah does not say this in opposition to God’s will, for he knew the Lord intended the contrary. Rather, his desire for peace must be understood as conditional—that is, “if God wills it.” In this way, he conforms his own will to the divine will, wanting whatever God wants to happen.

   Second, so that he would not seem to agree with falsehood, he proposes a sign of truthfulness: but hear. This sign is taken from Deuteronomy 18:22: whatever that prophet shall prophesy in the name of the Lord, and it does not come to pass, this the Lord has not spoken.

   However, Jeremiah himself seems to argue from the contrary, and this argument would appear to be invalid because it is the fallacy of denying the antecedent.In other words, it appears as if Jeremiah might be arguing as follows: if it does not come pass, then the Lord has not spoken; but it has come to pass (denying the antecedent); therefore, the Lord has spoken. The conclusion is formally invalid, as it does not demonstratively follow from the premises. This is because the opposite principle is found in Deuteronomy 13:1–3: if there arise in your midst a prophet, or one who says that he has seen a dream, and he should predict a sign and a portent, and what he says should come to pass, and he say to you, ‘Come, let us follow strange gods whom you do not know, and let us serve them,’ you shall not listen to the words of that prophet or dreamer.

   It must be said, however, that Jeremiah's argument is effective for exposing the false prophet’s deception, which is his intention.