RUSSELL SHORTO in The New York Times:
THE INVENTION OF AIR: A Story of Science, Faith, Revolution, and the Birth of America By Steven Johnson
The Age of Categories is dead. Strangely, it never went by that name, or any name. Also curious is the fact that its boundaries are unclear: it overlapped the Age of Enlightenment, the Age of Reason and some others, but succumbed to the atomizing atmosphere of the Information Age. Knowledge, it held, went hand in hand with nomenclature and delineation. As science developed, branches formed. Elemental to the college and university were academic departments, each of which came surrounded by high walls. A datum was deemed to fit within the confines of chemistry or sociology or the history of spoons or whatever, and that was more or less that.
Now we perceive the limitations of those old categories and scoff; we value multidisciplinarianism and genre-bending. The life of the mind is more chaotic, but also more exhilarating.
Often a new boundary-crossing perspective comes simply from going back to original sources — to the time before categories hardened. Study the famous late correspondence between Thomas Jefferson and John Adams, Steven Johnson notes, and you find only five references to Benjamin Franklin and three to George Washington, but 52 to Joseph Priestley, the scientist/theologian who is often credited with the discovery of oxygen.