I think the most weighty defence of the study of philosophy is one that I don’t hear very often. It’s a bold defence; perhaps too bold for many of us.
Ask any field of knowledge, “Why? Why do we believe that?” long and persistently enough and eventually they’ll all pass the buck. There are no sciences which contain within themselves their own complete justification, much as the odd scientist might feel otherwise.
And in this particular game, all roads lead eventually to philosophy. That’s just the nature of the topography. It’s the nature of how philosophy and other knowledges relate to one another.
This is not to deny that there are some philosophers who will attempt to bass the buck back eventually, announcing that it is physicists, or biologists, or psychologists, or literary theorists, etc, who have the truly original knowledge. Even in this case, however, it is the philosopher who is taken to have the expertise to be able to pronounce authoritatively about where our knowledge really comes from. This is just the internal logic of the whole system; philosophy exists, in one sense, in order for others to be able to pass the eventual buck.
I’ve spent a fair bit of time trying to remember what makes philosophy so attractive and compelling to me. It surprises me that it’s taken so long for me to arrive at this formulation; that’s not to say this is the final or highest reason to look to philosophy, only that I would have expected it to be a more obvious one, something that would suggest itself to me sooner.
One thing that’s compelling about this particular formulation is how it integrates how philosophy (at least implicitly) sees itself and how non-philosophers (at least implicitly) see philosophy. It’s good to start from an agreeable premise, even if that turns out not to be really what is first by nature.
I suspect that part of the reason why this approach didn’t come to mind for me is because of how the lines connecting philosophy to other fields have grown much weaker. You can’t rely on a given student of philosophy to be generally very knowledgeable about other fields (myself least of all, sadly). Philosophy is largely able to happen in isolation from developments in other realms of learning, and vice versa. They do intersect occasionally and in unpredictable ways, but it seems to me that without some greater integration than we really seem to have for now, this portrayal of philosophy, valid as it surely is, feels more like a sort of unrealized ideal.