“Because of its origins and guiding principles, symbolist machine learning is still closer to the rest of AI than the other schools. If computer science were a continent, symbolist learning would share a long border with knowledge engineering. Knowledge is traded in both directions— manually entered knowledge for use in learners, induced knowledge for addition to knowledge bases— but at the end of the day the rationalist-empiricist fault line runs right down that border, and crossing it is not easy.”