Gilson on History vs. History of Philosophy

An interesting comment from Gilson's preface to Owen's The Doctrine of Being in the Aristotelian Metaphysics, p. vi.

It may seem idle to say that the problem at stake in this book belongs to the history of philosophy, but it is not. To rediscover the thought of Aristotle in its purity is assuredly the work of an historian, using all the resources of modern historical methods, from philology proper to the widest possible critical discussion of the works already devoted to the same subject; but the history of philosophy also requires an historian with the mind of a philosopher, because, in such a case, the very object of history is philosophy, that is, a certain set of philosophical notions to be understood  by us in the very same sense which they once had in the mind of a certain philosopher. This is no easy task, but one is sure to miss the point completely if, while availing himself of all the possible sources of historical information, he forgets that the method of methods in the history of philosophy is philosophical reflexion.