Do philosophers of history operate on any kind of different modes of thinking or inquiry as compared to professional historians? One question I'm struggling to understand is just when if ever does studying history lead to normative ethics for the present day on how to act towards certain groups?

Interesting! In order to practice and contribute to the philosophy of history, philosophers need to know both a wide range of works of history as well as to know about the methods employed by historians, but they do not need to be historians themselves. So, in your terms, philosophers of history need not use the same "modes of inquiry as compared to professional historians." The same is true in, say, philosophy of art in general or philosophy of biology. In philosophy of history general questions are raised about truth, testimony, the meaning of events, the nature of causation and historical explanation, and so on. Professional historians may presuppose a philosophy of truth (etc) but in constructing the history of the French Revolution (for example), they need not engage in any explicit reflection on alternative philosophies of truth, testimony, etc. As for history leading to normative ethics, matters are complex. Arguably the practice of history itself will rest on some value judgements (even if it is the vague judgement that some events are more interesting to study than others). But apart from the values that are assumed as the motive for doing history, the practice of history may be ethically illuminating in many ways, including:

History provides us with the opportunity to learn of (and from) the moral thinking of others. For a great book on this, see Thomas Carson's Lincoln's Ethics, Cambridge University press. Brilliant!

Historical accounts may inform our assigning responsibilities for good or ill in the present. We may, for example, discover that some of us today have duties of compensation owed to others.

Historians may uncover cultures and traditions that offer us today cogent or challenging teachings about values that we have neglected

History may provide us with patterns we can learn from. I think that the architects of the western incursion into Iraq could have learned the imprudence of this act based on the study of similar invasions.

That is only a beginning. For an excellent introduction to philosophy of history, see History and Theory; Contemporary Readings ed. by Brian Fay, P. Pomper, and R.T. Vann.

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