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Thomas Jefferson, whose library became the core of the Library of Congress*, arranged his books into three types of knowledge, corresponding to Francis Bacon's three faculties of the mind: Memory (History), Reason (Philosophy) and Imagination (Fine Arts). At the time, there was no formal or standardized method for categorizing books. Most libraries at the time were arranged alphabetically but this system, while great for locating a specific known item, is not conducive for browsing or locating similar sources of a given subject.
On Memory, Jefferson wrote that "it is the duty of every good citizen to use all the opportunities which occur to him for preserving documents relating to the history of our country." Memory is the core of history, and shared memories constitute the core of a common national past.
In Jefferson's library, the category of Reason included government and law, science and invention, and the exploration and mapping of the natural world. Imagination included books on architecture, music, literature, and criticism has grown to include all forms of American creativity.


*After the British burned Washington, including the Library of Congress, during the War of 1812, Jefferson offered to sell, and Congress agreed to buy his collection of books to replace those lost.