Humans can not share Knowledge if they do not
speak a common Language. It is very important that understanding is only possible if one speaks a common Language.
Speaking a common Language means that one uses common Symbols and Concepts and this has to be defined with a common Syntax. On the other hand there must be an Agreement the Meaning of this Symbols and Concepts. So one has to define a Semantics. To this also belongs that the Concepts that are defined and talked about are classified somehow: What is a Subconcept and what is a Superconcept and how are they connected with each other? This can be done with the help of Taxonomies. One has also to state which things are related with other things and Concepts, i.e. what Associations are there and what Relations are there between Concepts. This can be found, for example, in an Thesaurus. If one has Relations and Associations between Concepts the next thing that one can do is to formulate axioms about certain Restrictions: When does a Relation make Sense and when does it not make Sense? What Restrictions are connected to a given Relation or Association? What makes Sense, what is True and what is not True? These Rules and these Axioms they have to be or can be expressed in the Sense of an Ontology or several Ontologies.
To speak a common Language...