As is well known the Enlightenment assumed in its confidence that only error and prejudice--above all religious superstition--block the path to the perfect society, where the timeless values of human existence will all be realized. Condorcet expressed this vision thus: "Nature binds by an unbreakable chain truth, happiness, and virtue." Condorcet's idea was that knowledge of the truth or the scientific study of man's place in nature and the workings of society provides the key to a world where virtue and happiness will thrive together. Ignorance, so he and other 18th-century thinkers supposed, is the great enemy of man's perfectibility.

Perfectibility implies the notion of the perfect whole the ultimate good, in which all good things coexist. As Charles Lamore says in his review of Isaiah Berlin's The Sense of Reality: Studies in Ideas and Their History Western philosophy has been predominately monist in character:

Since Plato, most philosophers have supposed that the proper ends of life all express or promote a single ultimate value, though naturally they have disagreed about what it is: rational thought, pleasure, perhaps freedom. None has denied, of course, that there are many different activities, traits of character, and states of mind that we rightly prize. But this multiplicity has not been thought to extend to the nature of goodness itself. Instead, the assumption has been that all these things are good because they draw in various ways upon a single source, a single ultimate good that defines what is of supreme moment in our humanity.

Pluralism for Berlin is the view that the ends which reasonable people may pursue are ultimately not one, but many. The forms of human good do not have a common source; indeed, they prove so divergent in their tendency that they defy unification within a single life--they may even prove irreconcilable within any given culture.