...it certainly has been an elusive goal...

In almost all philosophy doubt has been the goad and certainty has been the goal.  There has been doubt about the senses, doubt about science, and doubt about theology.  In some philosophers one of these has been more prominent, in others another.  Philosophers have also differed widely as to the answers they have suggested to these doubts and even as to whether any answers are possible.

-Bertand Russell, as excerpted from here