Begin with the concession, because it is the honest one and it costs us nothing. No, we cannot prove that the New Testament writers quoted from “the Septuagint” for the simple reason that in the first century there was no such book. There was no single bound volume, no fixed table of contents, no edition anyone could have handed St. Paul. What existed was a body of Greek translations of the Jewish scriptures, made by different hands across more than two centuries, circulating in competing revisions that already disagreed with one another. Asking which copy of “the Septuagint” St. Matthew owned is like asking which edition of “the English Bible” a Victorian preacher kept on his desk. The question assumes a thing that had not yet been assembled.

So set that question down and pick up the one underneath it, which is answerable: did the apostles quote a Greek Old Testament that differs from the Hebrew Bible printed in Protestant Bibles today? Yes. Demonstrably. And you do not need Greek, or Hebrew, or a scholar’s library to verify it — you need a Douay-Rheims and about ninety seconds.

Turn to Amos. The prophet says that Israel restored shall “possess the remnant of Edom” (Amos 9:12). Now turn to the Council of Jerusalem in Acts 15, where the apostles are deciding the single most consequential question the early Church ever faced: whether Gentile converts must be circumcised. St. James settles it by quoting Amos, and this is what comes out of his mouth: “That the residue of men may seek after the Lord, and all nations upon whom my name is invoked” (Acts 15:17). Not a paraphrase. A different text.

The mechanism is not mysterious, and it is not a corruption. Ancient Hebrew was written without vowels. The letters behind they shall possess and they shall seek differ by a single consonant, and the identical consonants of Edom also spell man. One tradition read and pointed those letters one way, the Greek translators had read them the other, centuries before Christ, with no Christian axe to grind. And St. James’s argument works only on the Greek reading. A prophecy that Israel will possess Edom does not establish that the nations are to be received without circumcision. A prophecy that the residue of men will seek the Lord does exactly that.

Sit with the consequence. The first doctrinal decision in the history of the Church, the decision that opened Christianity to the whole world rather than leaving it a sect within Judaism, was argued from a Greek Old Testament, against the reading that the Hebrew text would later carry. If the Masoretic Text is the only authentic Old Testament, then the apostles reasoned from a corruption, and got the right answer anyway. That is a heavy price to pay for a tidy theory of the canon.

Now the concession that most Catholic tracts will not make, and we will make it in our own voice: none of this puts the deuterocanonical books into the apostles’ hands. The New Testament never once formally cites Tobias, Judith, Wisdom, Sirach, Baruch, or the Maccabees with “it is written.” Anyone who tells you otherwise is overselling, and you should not repeat it. What the New Testament does is echo them; the mockers at the Cross speak Wisdom 2 almost word for word1; Hebrews 11:35 remembers the mother and her seven sons of 2 Maccabees. Echoes are real evidence of what the apostles read. They are not proof of a canon. And the price of that argument is a verse most defenders skip: St. Jude says that “Enoch also, the seventh from Adam, prophesied” (Jude 14), quoting a book no Church of the West or the Byzantine East has ever received as scripture, and which is canonical today only in the Ethiopian Tewahedo tradition.

Which is the whole point, and it is where the objection quietly collapses. The canon was never going to be read off the spine of a book, because there was no such book, on either side. The Dead Sea Scrolls settled that. Among them are Hebrew manuscripts agreeing with the Greek against the later Hebrew text, which means that where the Greek translators produced a reading that afterwards looked like a mistake, they were often rendering a genuine Hebrew text that later fell out of use. Those manuscripts are a minority of the collection: what they vindicate is the translators’ integrity, not the supremacy of their Greek. But the consequence still stands — “the original Hebrew Bible Jesus used” is not a thing anyone can produce. It, too, was still being settled.

So the apostles had no closed canon. They had scriptures (plural, fluid, circulating in more than one language and more than one text-form), and they had a Church with the authority to discern. Every Christian alive today reads from a table of contents that somebody had to recognise. The only live question is who was given authority to discern it2, and that question a book can never answer, because no book contains its own index.

The full case (every disputed quotation weighed, including the ones that cut against us3) is set out at length below.