The document discusses implementing common sense in expert systems. It explains that expert systems currently lack common sense because they only know equations and variables, not real-world knowledge. This knowledge is needed to perform human-like reasoning. The document proposes representing this knowledge as formal ontologies - sentences in logical language that describe concepts and relationships in a domain. However, building complete ontologies is challenging due to the vastness of common sense knowledge and tediousness of the knowledge engineering process. The document also discusses representing knowledge as a graph and how this could help computers better understand language and perform common sense reasoning.