I got the following in an email from Gary Michuta, who is an expert on these matters:
The Canon and the Council
Refuting the Argument that Canon was not established until the Council of Trent
By Gary Michuta
Today, some Protestants are arguing that Luther did not subtract books from the Canon of Scripture, because the canon was not officially adopted until the Council of Trent which began in 1545. Since the canon was not formally recognized prior to Luther’s rejection of the Deuterocanonicals, it is not correct to say that he subtracted books from the Bible.
This type of argument is quickly beginning to become a favorite among our separated brethren. They want to divert attention away from how these books were accepted within Christianity and focus instead on technical language in regards to their definition by the Church.
The fact of the matter is that even if something like the definition given at Trent had happened before Luther’s day, Luther would have rejected it as being in error, and Protestants wouldn’t have abandoned Luther because of his position any more than they abandoned Luther when he brushed aside other councils. In other words, this argument really isn’t about the legitimacy of the Protestant position, but rather it is a form of propaganda to make it look like the Church is dishonest.
However, what about the claim? Here is my two cents on the matter: After St. Jerome became the first Christian to cause a major stir by attempting to reject the Deuterocanon as Apocrypha, there were a series of local councils that met in North Africa to reaffirm the Christian Old Testament and New Testament. These were the councils of Hippo (393), Carthage I (397), and Carthage IV (419). All three of these reaffirmed the Catholic canon as canonical and divine Scripture. However, they were local councils that were confirmed by the Pope. Therefore, they were authoritatively defined but not with the solemnity of that of an Ecumenical Council. You must remember, however, that solemnity does not effect the authority of the definition given. Usually Ecumenical Councils met to address something that has disturbed the universal Church. By the end of the fourth century, Jerome’s views had caused trouble mainly in North Africa. Regardless of their solemnity these councils are the first to authoritatively define the canon. After them, Innocent I (417) was questioned by a bishop as to the canon and Innocent’s reply repeats the decree of Hippo / Carthage. This is the first Papal decision on the canon. There were a series of decrees attributed to Popes Damasus, Gelasius, and Hormisdas between 266-523 that also reaffirmed the canon as well. By the end of the ninth century, Pope Innocent I could write to the bishops of Gaul (modern day France) that the letter of Pope Innocent I on the canon was the “universal law of the Church.” To this, we could add that there are about a dozen local and regional councils (not to mention popes) during this period who issued decrees that quoted the Deutero’s to confirm doctrine and with the formal introduction normally given to Scripture showing that the issue was largely settled and that bishops throughout the world were confident in appealing to these texts.
Probably the most important council to bring up is the Council of Florence, which promulgated a decreed on canon of Scripture on Feb. 4, 1441. Florence’s decree states that the Catholic canon is given by the Holy Spirit and the Church accepts and venerates them. In terms of solemnity, this decree is greater than the previous ones. However, in terms of authority it is just as authoritative as the rest.
In 1519, Johann Eck debated Luther and pointed out to him that the Church had already confirmed that the Deuterocanon was canonical Scripture and he explicitly cited Florence as a proof of this. What was Luther’s response? Was it that the Church has authoritatively defined the canon yet so everything is still up for grabs? This is what the Protestant historian H. H. Howorth says about what Luther said:
“He [Luther] says he knows that he Church had accepted this book [2 Maccabees], but the Church could not give a greater authority and strength to a book than it already possessed by its own virtue.” (Gary Michuta, Why Catholic Bibles Are Bigger, p. 251).
So, Luther knew the Church accepted the Deuterocanon as canonical Scripture. He was aware of Florence and the other decrees (apparently), but by this point he believed that Church councils could err. Moreover, Luther seems to have been working on a principle that he would more explicitly develop a few years later; namely, that a book is canonical and authoritative to the extent that Luther heard “Christ preached” in it.
Now what about Trent? Why do all these sources say that it wasn’t until Trent that we had a definitive decision on the canon? First, the fathers at Trent decided early on to adopt the canon of Florence without comment. For them, the issue was already closed in previous councils. However, since some otherwise solid Catholics have seem to adopted Jerome’s views on the Deuterocanonicals over and against these previous councils something more was necessary to drive the point home that the matter has already been closed hundreds of years early. So, Trent attached an anathema to its decree on the canon. Trent wasn’t the first council or Church authority to define the canon, but it was the first to anathematize those who did not follow the canon. In terms of the authority of the canon, nothing was really changed, but the solemnity of Trent’s definition was, because of the anathema, far greater than any previous council.