The Biblical Canon of
Athanasius of Alexandria

The Canon of Athanasius of Alexandria can be found in his 39th Festal Letter, written in 367, and is widely regarded as a milestone in the evolution of the canon of New Testament books. Athanasius is the first person to identify the same 27 books of the New Testament that are in use today. Up until then, various similar lists of works to be read in churches were in use. Athanasius compiled the list to resolve questions about such texts as the Epistle of Barnabas. Athanasius includes the Deuterocanonical (Apocryphal) Book of Baruch and the Letter of Jeremiah, but places the Book of Esther among the “7 books not in the canon but to be read” along with the Deuterocanonical books of Wisdom of Solomon, Book of Sirach, Book of Judith, Book of Tobit, the Didache, and The Shepherd of Hermas;

“But for greater exactness I add this also, writing of necessity; that there are other books besides these not indeed included in the canon, but appointed by the Fathers to be read by those who newly join us, and who wish for instruction in the word of godliness. The Wisdom of Solomon, and the Wisdom of Sirach, and Esther, and Judith, and Tobit, and that which is called the Teaching of the Apostles, and the Shepherd. But the former, my brethren, are included in the canon, the latter being read; nor is there in any place a mention of apocryphal writings. But they are an invention of heretics, who write them when they choose, bestowing upon them their approbation, and assigning to them a date, that so, using them as ancient writings, they may find occasion to lead astray the simple.”
-Thirty-Ninth Festal Letter from Johannes Kirchhofer, Quellensammlung zur Geschichte des Neutestamentlichen Kanons bis auf Hieronymus (Zürich: Meyer and Zeller, 1844), 7-9.

He does, however, rely heavily on the Deuterocanonical books and other religious literature not found in his canon list in similar ways to how he cited canonical literature -even referring to them as Scripture;

“And this difference divine Scripture recognises, saying concerning the creatures, ‘The earth is full of Your creation,’ and ‘the creation itself groans together and travails together;’ and in the Apocalypse it says, ‘And the third part of the creatures in the sea died which had life;’ as also Paul says, ‘Every creature of God is good, and nothing is to be refused if it be received with thanksgiving;’ and in the book of Wisdom it is written, ‘Having ordained man through Your wisdom, that he should have dominion over the creatures which You have made’ [Wisdom 9:2.]” -Four Discourses Against the Arians, 2:45

Athanasius was the first to used the phrase “being canonized” (kanonizomena) in regard to books sanctioned by the Church as Scripture and is where we derive the modern English word canon from the Greek κανών kanōn, meaning “rule” or “measuring stick”. From his use of other literature, however, it’s clear that Athanasius himself did not regard the “canon” as a closed list to the exclusion of all else, but rather as a “measuring stick” on which to grade other writings.

Sources: 

• Edmon L. Gallagher and John D. Meade. The Biblical Canon Lists from Early Christianity:  Texts and Analysis.  Oxford University Press. 2017
• Michuta, Gary. Case for the Deuterocanon:  Evidence and Arguments.  Nikaria Press, 2015.