Theory of Probability is distinguished by several high-level philosophical attitudes, some stressed by Jeffreys, some implicit. By reviewing these we may recognize the importance in this work in the historical development of statistics.
"Comment: The Importance of Jeffreys’s Legacy." Statist. Sci. 24 (2) 179 - 182, May 2009. https://doi.org/10.1214/09-STS284A