Full Idea
There are four uses of the word "is" in English: as existence ('he is at home'), as predication ('he is tall'), as identity ('he is the man I saw'), and as classification ('he is British').
Gist of Idea
Note that "is" can assert existence, or predication, or identity, or classification
Source
PG (Db (ideas) [2031])
Book Reference
A Reaction
This seems a nice instance of the sort of point made by analytical philosophy, which can lead to horrible confusion in other breeds of philosophy when it is overlooked.