e tend to think of philosophers as solitary creatures. Whether it be Diogenes or Socrates, Spinoza or Rousseau, Thoreau or Nietzsche, the philosopher is by necessity a loner. Several recent books, however, remind us that philosophers can also travel in packs. Not the packs that wear lanyards at academic conferences, mind you, but those that form in spite (or defiance) of the academy. David Edmonds's and Karl Sigmund's are sharp accounts of the Vienna Circle, the group of European thinkers who founded the club of logical positivism (one that their idol, Ludwig Wittgenstein, refused to join). Another pair of books—Clare Mac Cumhaill and Rachael Wiseman's and Benjamin J. B. Lipscomb's —offer insightful and often moving portraits of
