Specialization is inherent in scholarship, and the patterns of development are similar in all fields. Scholars seek the company, approval, and criticism of those who understand what they are doing; the closer the specific subject area of one scholar to that of another, the better the two can understand each other. When a field or discipline begins to emerge, its scholars must be satisfied with the collegiality of those working in related but distinctively separate areas. As time passes, the members of a discipline who are interested in similar, closely related topics increase. They develop close intellectual bonds. When a sufficient number define their field of endeavor in the same terms, a subfield, a specialization, has been created. Subfields may in turn generate their own subfields, but all are part of the same system. Scholars have, nevertheless, found less and less in common with those working outside their own specialized subfield.
In history, it is impossible to assign precise dates to the beginning of specialization because every historian is in some sense a specialist. A mature discipline, in which various subfields have replaced the field in general as the area of activity, in which subfields have established priorities and historians are working on the problems, is a product of the second or third generation of professional historians. Only then do they think of themselves as American historians or economic historians rather than as historians.