When it comes to defending the canonicity of the Deuterocanonical works, some pop Catholic apologists often appeal to the Septuagint (LXX) as the LXX, purportedly, contain these works. The reasoning goes that, as the LXX was “the Old Testament” of the earliest Christians, ipso facto, the Deuterocanonical works were accepted as being equally authoritative as the other books in the Old Testament.
There are many problems with this line of reasoning, including the fact that there was no one type of Septuagint, and many contained different listings of books, including some not accepted as canonical by Trent in its infallible decree in April 1546 (e.g., 1 Clement). As one Catholic Bible wrote in the preface to its translation of 1-2 Esdras and the Prayer of Manasseh:
SOME ADDITIONAL BOOKS
INTRODUCTION
1 Esdras, 2 Esdras, and the Prayer of Manasseh are accepted by many Protestants and Anglicans as being part of the Apocrypha. They are not accepted as canonical by Roman Catholics. 1 Esdras and the Prayer of Manasseh constituted a part of the Septuagint Greek text of the Old Testament used by Christians during the early centuries of Christianity. The book of 2 Esdras may not have been in its final form until toward the end of the second century AD. (Good News Bible with the Deuterocanonical Books also called The Apocrypha [2d ed.; The Bible Societies/Harper Collins, 1994], emphasis added)
In this instance, appealing to the LXX without qualifications and nuances as more informed Catholic apologists do, puts the Catholic apologist in the unenviable position of having, if they wish to be consistent, to (1) admit that Trent was wrong in not accepting the canonicity of 1-2 Esdras and the Prayer of Manasseh or (2) that the common manner of appealing to the LXX is errant.
As I stated above, there are more informed Catholic approaches to this issue, most notably the works of Gary Michuta, such as:
Why Catholic Bibles are Bigger (2d ed.) and
The Case for the Deuterocanon: Evidence and Arguments
While I disagree with his conclusions, Michuta does a very good job in many areas, including refuting the common Protestant abuse of Luke 24:44 (some have even used this as evidence for Sola Scriptura during the time of Jesus!). I just mention this as I do not wish to beaccusedd of ignoring the better arguments for the Apocrypha/Deuterocanonical works forwarded by informed Catholic apologists.
As an aside, Michuta engaged James White in a debate on this issue back in 2004--it is worth watching (White relied upon the arguments of William Webster, which was unfortunate, as Webster is a poor researcher--he should have relied upon Roger Beckwith's 1985 The Old Testament Canon of the New Testament Church as he did in another debate with Gerry Matatics in 1993, even if one finds Beckwith's arguments at times to be strained):