Gregory was born to Mary Jones and Henry Duval Gregory in
Philadelphia. He was the brother of the American zoologist
Emily Ray Gregory. After completing his bachelor's degree at the
University of Pennsylvania in 1864, he studied theology at two Presbyterian seminaries: in 1865—1867 at the
Reformed Presbyterian Theological Seminary, Philadelphia, and in 1867–1873 at the
Princeton Theological Seminary. In 1873, he decided to continue his studies at the
University of Leipzig under
Constantin von Tischendorf, to whose work on textual criticism of the New Testament he had been referred by his teacher
Ezra Abbot. He administered the scientific legacy of Tischendorf, who died in 1874, and continued his work. In 1876, he obtained his
PhD with a dissertation titled
Grégoire the priest and the revolutionist. The first examiner for it was the historian
Georg Voigt. He completed his post-doctoral work in Leipzig in 1884, and became an associate professor in 1889 and a full honorary professor in 1891. That same year, he was elected an International Member of the
American Philosophical Society. He apparently had several doctorates: Karl Josef Friedrich (p. 130) even mentions five doctorates in his biography of Gregory. At least one doctorate in theology obtained in Leipzig in 1889 is attested. In June 1901, he received an honorary
doctorate of Divinity from the
University of Glasgow. On August 11, 1914, Gregory, who had been a citizen of
Saxony since 1881, enlisted in the
German Army as its oldest wartime volunteer. He became a second lieutenant in November 1916 and died on April 9, 1917, in a
field hospital in
Neufchâtel-sur-Aisne,
France. Gregory specialized in New Testament
textual criticism. He organized biblical manuscripts into a classification system (
Die griechischen Handschriften des Neuen Testaments, 1908) which continues to be in use throughout the scholarly world today. He is also credited with being the first to notice the consistent medieval practice (called Gregory's Law or Gregory's Rule) of collating parchment leaves so that grain side faced grain side and flesh side flesh side. He was also interested in
biblical canon. == Works ==