Richard Marshall interviews Dennis Rasmussen in 3:AM Magazine:
Dennis Rasmussen: It does seem pretty remarkable that two thinkers of this stature were best friends for nearly their entire adult lives and yet no book had been written on their personal or intellectual relationship. I can think of a couple of likely explanations for this. The first is simply that their lives – especially Smith’s – aren’t nearly as well documented as one could wish. There are only fifty-six surviving letters between them, and many of these are fairly short and mundane, though others are quite humorous, intellectually substantial, and/or revealing about their characters. I try to provide the fullest possible account of their friendship based on the record that does exist – in these letters, their published works, the testimony and correspondence of others, and the periodicals of the day. I think there’s enough there to tell a compelling story, even without resorting to the kind of speculation that often tempts historians when sources are thin.
Another likely reason why Hume and Smith’s friendship hasn’t received sustained analysis is that friendships are more difficult to bring to life than quarrels: conflict makes for high drama, while camaraderie doesn’t. So it’s not surprising that there have been many books written on philosophical clashes – think of David Edmonds and John Eidinow’s Wittgenstein’s Poker and Rousseau’s Dog, Yuval Levin’s The Great Debate, Steven Nadler’s The Best of All Possible Worlds, Matthew Stewart’s The Courtier and the Heretic, and Robert Zaretsky and John Scott’s The Philosophers’ Quarrel, to name only a few recent titles – but far fewer on philosophical friendships. The relative lack of attention paid to philosophical friendships, while understandable, is unfortunate, especially since friendship was seen as a key component of philosophy and the philosophical life from the very beginning, as even a cursory reading of Plato or Aristotle should remind us.
More here.