I think at least two of the explanations dismissed by the author are intriguing, even if not fully adequate as answers to her question. >Philosophy is not tryi

I think at least two of the explanations dismissed by the author are intriguing, even if not fully adequate as answers to her question. >Philosophy is not trying to communicate normal content that can be in explicit statements, of the kind you might be able to explain well and check the understanding of and such. I think there's something to that. Some forms of philosophy advocate broad conceptual systems that "hang together" in a way. I don't know how you would teach Kantian philosophy without reading passages from Kant, for instance. >Philosophy is about having certain experiences which pertain to the relevant philosophy, much like reading a poem is different to reading a summary of its content. I think that applies to writers such as Nietzsche, and some of the more substantive writers continental philosophers. It also applies, for better or worse, to writers who in my opinion wrote nonsense, but are nevertheless written in a style intended to be "experienced." And at least in principle I don't think there's anything wrong with that. And beyond those two bullet points, I can think of a few more. One is we're supposed to believe that philosophy deals with timeless subject matter. So it's not necessarily surprising that at certain points in history some people might do a really good job writing about it, expressing ideas that continue to be relevant and which aren't improved upon by attempts to elucidate. Another reason to read old philosophers is the same reason some courses teach math or physics in a way that emphasizes the historical circumstances where the ideas first originated. I've even heard of some courses that teach almost entirely in primary sources. You can view the ideas with a sense of discovery and an appreciation for the ingenuity involved. A lot of the magic in very beautiful ideas tends to die when it's clinically summarized in a textbook. Now, all of that said, I still think there are many branches of philosophy where you don't need to read old sources. Things like language, logic, meta-ethics, and probably many others can just be summarized while ignoring historical sources, saving a lot of time. But again, contra the author's suggestion, from what I know it's at least relatively common to have graduate level courses on philosophical subjects that are focused on cutting edge literature.