There was an interesting question raised on Twitter recently:
The Journal of the History of Philosophy just published an article on Quine. Not at all a dig at this author or this paper, but I'm a little surprised that someone as recent as Quine counts as history of philosophy. How old does a text have to be for it to be history?
— Sam Director (@sam_director_) October 7, 2022
The tweet's formulation of the question unfortunately is just one example of a common misunderstanding people, including professional philosophers (who are more easily misled by labels than they like to pretend), have about the field of history of philosophy (HoP) -- that it is, as a field, history. It is not; it is, as a field, philosophy. Thus the question of relevance is not, "How old does a text have to be for it to be history?", for which you should ask the history department, but instead, "How old does a text have to be for it to be history of philosophy?" And the answer is that it doesn't have to be any kind of old to be something studied in history of philosophy. It just has to occur at some time the entire history of the world as it is or as it could have been or as it will be. Obviously, our ability to study texts that don't exist yet is very limited and usually confined to genre issues or general and abstract questions of how schools relate to each other; and obviously most of the actual counterfactual work in HoP is concerned with helping clarify the actual course of philosophy through history, but HoP covers the entire history of philosophy insofar as it can be covered by evidence we have -- and note that I say that it covers the entire history, not 'the entire past'.
In general, there are three major interests in HoP; you get them in different mixes, both across individuals and across the different topics in the field.
(1) The diachronic and transpersonal life of arguments. If an argument has different effects through time (e.g., people responding to or influenced by it) or is communicated from one person to another, it has a history. Historians of philosophy study all the same arguments any other philosopher does, but they study them insofar as they have a history. A byproduct of this is that historians of philosophy are often much more concerned with evidence about arguments than some; they want to know what the evidence shows to be the actual life and history of arguments. For most philosophical arguments we actually know, the evidence is obviously going to be historical in the sense of being evidence about the past.
(2) The big-block historical elements of philosophy. Many academic philosophers spend their careers mostly looking at individual arguments one at a time, but a lot of us are interested in philosophy at larger scale -- not just individual arguments but schools, movements, networks of influence. This still involves a lot of looking at individual arguments, but historians of philosophy study them insofar as they contribute to much bigger blocks than themselves.
(3) The person as source and transformer of philosophical reasoning. Many academic philosophers look at arguments purely formally -- the argument as formulated in a specific artificial and natural language, without regard for its larger causal account. Historians of philosophy do not confine themselves to purely formal consideration of argument; they also look at the arguments insofar as they have a source, insofar as they have a purpose, insofar as they are constricted or made possible by their materials, insofar as they are affected by constraints of social and mental environment, and so forth. Thus historians of philosophy, while not as such interested in pure biography, are interested in the biographical aspects of how arguments develop, change, and influence.
Therefore, if the argument exists over time, it falls under history of philosophy. If the argument is part of a movement or school or chain of influence or something like that, it falls under HoP. If it is put forward by or modified by people, it falls under HoP. It follows from this that literally everything in philosophy is something that is or can be studied by historians of philosophy, every philosophical topic, every philosophical argument, every philosopher. What distinguishes the historian of philosopher is the reduplication: what HoP studies is studied as existing through time, as part of a movement, as proposed or modified by persons.
Historians of philosophy do often use what we might call historical methods, digging into archives, finding original readings, and things like that, but this is not something done consistently across the field, because it's not done for its own sake. It's a means to doing philosophy. Likewise, HoP has a lot of points of connection and overlap with its closest cousin in the field of historical scholarship, usually known as the history of ideas (particularly when looking at how social and material infrastructure affect or are affected by philosophical reasoning); but history of philosophy is not history of ideas. The historian of philosophy is a philosopher, not a historian.
