Pre internet book authors generally churn out higher quality efforts because they were forced to take more time and had to look for a publisher who recognized the merit of their work. Such a book is The Metaphysical Club written by Louis Menand in 2001. Farrar, Straus and Giroux NYC bet Menand would produce a quality tome that would withstand the test of time.
Walt Whitman must have been a nominalist based on how Menand defined it. It is the view that since concepts are frequently generalizations about collections of individual events or outcomes, they do not refer to anything that is real. It is only humans interpreting these events that leads to the declaration of the concept that props it into existence.
To generalize is to be an idiot is often attributed to Mr Leaves of Grass, so I am guessing he and Menand would have spent time at Star Bucks if they were still alive.