Look at the lattice of types from the previous page:
"Types in a lattice"
An individual from any of the groups that these types define can be the referent of a concept. For example:
This concept says that "There exists a person whose name is John". "Person" is the type, while "John" is the referent. In other words, "John" is the particular individual (or referent) which we are referring to, and he is an instance of the type "Person".
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Up: 3 Concepts
Next: 3.3 Examples