•  Most—but importantly but not all of that knowledge (see below)—is likely to be 

learned. No human is born knowing that lighters start fires, nor that dry cotton balls 
do not, nor what a glass bottle might do when it is broken. One might conceivably 
hard-wire that knowledge into an AI system, along the lines of CYC manually hard-
wiring each fact, but modern enthusiasts of machine learning would obviously prefer 
not to.  And because there is always new knowledge to be gleaned, mechanisms for 
learning new abstract, often causal knowledge are a necessity. 

•  Some significant fraction of the knowledge that a robust system is likely to draw
The Next Decade in AI-