Even in CYC's ability to reason, there is no doubt plenty of room for improvement. Its 
representations are primarily (or perhaps entirely) the stuff of higher-order logic; it's 
not clear to what degree it can represent uncertainty, and reason over statistical 
distributions, and so forth. As Bertrand Russell once put it, "All human knowledge is 
uncertain, inexact, and partial” and it's not clear how much of that uncertainty, 
incompleteness and inexactitude CYC can deal with.14  

And one suspects that, like much else in classical and neural AI, it is likely to be brittle, 
highly dependent on both the specific knowledge in its databases and the precise ways 
in which a complex scenario is mapped onto its internal logic.
The Next Decade in AI-