We met a coach loaded with passengers both within and without. Said I, "I defy all the philosophers in the world to tell me why this is." "Because," said Erskine, "the people wanted a quick carriage from one place to another." So very easily are the most of the speculations which I often perplex myself with refuted. And yet if some such clever answerer is not at hand, I may puzzle and confound my brain for a good time upon many occasions. To be sure this instance is too ludicrous. But surely, I and many more speculative men have been thrown into deep and serious thought about matters very little more serious. Yet the mind will take its own way, do what we will. So that we may be rendered uneasy by such cloudy reveries when we have no intentionto be in such a humour. The best relief in such a case is mirth and gentle amusement.
What pulled me up on reading this is how like Hume it sounds. To be sure, Hume has more serious perplexities in mind than Boswell's obscure puzzlement about the carriage; but the remedy of 'mirth and gentle amusement' is very Humean. Compare it with this well-known passage from Treatise 1.4.7:
The intense view of these manifold contradictions and imperfections in human reason has so wrought upon me, and heated my brain, that I am ready to reject all belief and reasoning, and can look upon no opinion even as more probable or likely than another. Where am I?, or what? From what causes do I derive my existence, and to what condition shall I return? Whose favour shall I court, and whose anger must I dread? What beings surround me? and on whom have I any influence, or who have any influence on me? I am confounded with all these questions, and begin to fancy myself in the most deplorable condition imaginable, environed with the deepest darkness, and utterly deprived of the use of every member and faculty.
Most fortunately it happens, that since reason is incapable of dispelling these clouds, Nature herself suffices to that purpose, and cures me of this philosophical melancholy and delirium, either by relaxing this bent of mind, or by some avocation, and lively impression of my senses, which obliterate all these chimeras. I dine, I play a game of backgammon, I converse, and am merry with my friends; and when, after three or four hours' amusement, I would return to these speculations, they appear so cold, and strained, and ridiculous, that I cannot find in my heart to enter into them any further.
It is possible that Boswell is influenced by Hume on this point; but it could well be that the similarity should be traced to a common source. It's an intriguing issue; and one of the things I enjoy about History of Philosophy. One of the neglected areas of HoP that I find fascinating is the study of how philosophical ideas diffuse through society; i.e., not just philosophical texts, but how they impact the world around them (and are impacted by it). I'm currently reading Sterne's Tristram Shandy; and one of the fascinating things about it, for me, (beyond the fact that it is just a great novel in its own right) is the way in which it, as light, satirical literature, interacts with the philosophical thought of the day. It's a bawdy, humorous story, intended for casual reading; but it doesn't take much to find interactions with, and satires of, Lockean or Baconian philosophical positions (for instance). This is a fascinating phenomenon the historian of philosophy should take an interest in: the adoption, and adaptation, of philosophical positions in novels, poems, sermons, newspaper articles (like the Spectator or the Idler), correspondence, private journals, dictionaries and encyclopedias (like Chamber's Cyclopaedia), pamphlets, and the like. We do, of course, look at some of this; but I can't help but fill that we would be greatly enriched by better understanding these aspects of ideas in motion. Very often, HoP is treated as a matter of getting an author right; but it should be part of our discipline to look at the diffusion of these ideas as well, in itself, and not merely as part of getting the author right.
After all, if interest in the diffusion itself is not enough, people like Hume did not write books in order that those books might exist as self-contained units, or that they might exist as part of an oeuvres complètes; they wrote books that they wanted to be read. (If you haven't already, you should read Hume's little autobiographical essay, written the year of his death.) They wrote letters to discuss ideas. They wrote sermons (well, Hume didn't write sermons, but others did) to edify and teach their congregations. And their books were often read; their letters often answered; their sermons often heard. Hume wanted to make an impact on society at large; it's why he wrote works like the Essays or the Enquiries. People like Descartes weren't writing for philosophers alone; as an unfinished Cartesian dialogue makes clear, part of the value Descartes saw in his philosophical approach was that it made philosophy more accessible to ordinary people. The life's work of these philosophers wasn't a set of arguments on paper; their life's work was the use to which they wanted to put those arguments, and the purpose for which they crafted those arguments, and the effects that they hoped those arguments would have. That is what makes a philosophical text. And so the philosophical text itself begs us, demands of us, that we take the time and see: How did it move out into the world? How did its arguments and concepts spread? How did it affect the society to which it belonged?