The philosophy of history is challenged to discover and explore the most fundamental questions about historical inquiry and knowledge. How should this research be conducted? And how should the philosopher's development of the subject make use of the practice of the historian? Look at this question from the point of view of the historian, and we will find that the separation between "doing" and "reflecting upon" history is not as sharp as it might appear.
For the best historians, there is no recipe for good historical inquiry and exposition. There are methods and practices of archival research, to be sure, and there are general recommendations like "be well informed about existing knowledge about your subject matter." But the great historians take on their subjects with fresh eyes and new questions. They often arrive at novel ways of framing their historical questions; they find new ways of using available historical evidence, or finding new historical evidence; they discover new ways of drawing inferences from historical data; they arrive at new ways of presenting their knowledge and narratives; and they question existing assumptions about "causation," "agency," or "historical period." As the historian grapples with the topic of research and the evidence that pertains to the topic, he or she is forced to think creatively about issues that go to the heart of historical inquiry and reasoning. In other words, the historian is forced to think as a philosopher of history, in order to achieve new insights into the problems she considers.
There is a less creative approach to historical research, of course. One can choose a familiar topic; seek out some new sources that have not yet been fully explored; adopt some familiar theoretical motifs; and place the findings into a standard narrative for publication. This mechanical approach resembles "normal science" for historians. But the results of this type of approach are inherently disappointing; it is unlikely in the extreme that new historical insights will emerge.
So when we consider the work of really imaginative historians, we find that the researcher is functioning as a philosopher of history at the same time as he or she is developing an innovative approach to the historical question under examination. And this means that the philosopher can gain great insight by working very carefully with the writings of these great historians. The philosopher can probe questions of historical inquiry, historical reasoning, historical presentation, and historical knowledge, by thinking through these questions in conversation with the working historian.
Consider a few examples that illustrate this productive possibility. First, consider the evolving state of affairs in historical treatments of the French Revolution. In the past forty years historians have taken a shifting series of perspectives on the events, social conflicts, cultural circumstances, and political realities of the Revolution. New research and new narratives have emerged on the Ancien Regime, the revolution, the Terror, and the consolidation of power by Napoleon. Fertile historians such as Soboul, Cobb, Darnton, Schama, Sewell, or Chartier have tested and explored a variety of new perspectives -- from Marxism, from social history, from cultural studies. And they have provided a much more nuanced body of knowledge about the social and cultural reality of the Revolution. This body of work provides a rich domain of conceptual and historiographical material for the philosopher of history.
A second example is the lively debate that has occurred about comparative economic history of England and China. In the past 15 years historians of Chinese economic history have challenged standard models of economic development and have argued for a more balanced comparative economic history for Eurasia. This debate has moved into great detail in the effort to answer such basic questions as whether China's agricultural economy was declining, static, or rising in productivity in the 17th century; or whether the standard of living was higher or lower at opposite ends of Eurasia. Once again, a philosopher of history can find great stimulation to further conceptual and philosophical research by studying this debate in detail; the debate provides a living example of how historical knowledge is born.
So my answer to the primary question here is this: that the philosophy of history needs to be fully immersed in some specific historical debates involving the most creative and imaginative historians. Careful study of these debates and sustained interaction with historians like these will lead in turn to much more developed understanding of the nature of historical reasoning.