This note does not aim to discuss definitions of “philology.” It merely aims to record Prof. Isaacson’s one of many possible definitions of it. On Thursday (30.11.2017), in his reading class on the Āmnāyamañjarī, he stated in passing that “philology is the art of distinguishing the probable from the possible.” After the class, we had our regular ITLR editorial meeting. In passing, I told him that I liked his definition of “philology.” He was not sure who formulated it for the first time. Just now, I see that Prof. Okita in his book refers to Prof. Isaacson’s 2007 lecture on “Philology and Codicology.” See Kiyokazu Okita, The Rise of Devotionalism and the Politics of Genealogy. Oxford Theology and Religion Monographs. Oxford: Oxford University Press, 2014, p. 18. The definition recorded by him does not contain the definitive articles before “probable” and “possible.” Articles seem necessary but I am not sure. I do not recall if I attended his 2007 class on “Philology and Codicology.” If I did, it is very embarrassing, for I have missed the jewel then. But I am glad that I have the jewel now. Better late than never.