 Two facts must be clearly recognized if a proper evaluation of the Vienna Circle is to be attempted. The first is, that, despite its relatively short existence, even some of the most central theses of the Vienna Circle underwent radical changes. The second is that its members were by no means of one mind in all important matters; occasionally they espoused perspectives so radically at variance with each other that even their ostensive agreements cannot remain wholly unquestioned. Behind the rather thin public front, then, quite different philosophical projects were being pursued by the leading participants with, moreover, changing alliances. One way of taking account of this is by speaking (as above) explicitly of the philosophies (in the plural) of the Vienna Circle (and to avoid the singular definite description) while using the expression “Vienna Circle philosophy” (without an article) in a neutral generic sense.