Open problems in AI

At a website called Apperceptual I came across a list of 21 open problems facing Artificial Intelligence research. I've listed them below, but I recommend that you visit the site for more information about each problem.

Symbol Grounding Problem
Frame Problem
Frame + Symbol Grounding
Variable Binding Problem
Self-Reference and Self-Modifying Algorithms
Connection between Symbolic and Subsymbolic Cognition
Best Method for Knowledge Representation
Foundation of Unsupervised Learning
Integrating Multiple Models, Multiple Resolutions (Granularities), Multiple Senses (Modes)
Belief-Action-Desire Model
Approximate Database Retrieval
Ethical AI
Integrating the Subfields of AI
Learning Physical Skills
Credit Assignment Problem
Non-Monotonic Reasoning Problems
Problems with Negation as Failure
Common Sense
Learning Chess
Raj Reddy’s Problems and Grand Challenges
Grand Challenges