I've been facinated by to-be as a word since I started learning Spanish and noticed that Ser and Estar can be used to separate out a temporary and permanent state of being; "I am sad" has an implicit temporary nature to it (rather than the permanence that can be implied with English).

Forms of 'to be'

The Wikipedia article on E-Prime calls out a number of different uses of 'to be' that impressed me, as I'd not thought about how many variable uses it has!

  • identity (noun-phrase copula definite-noun) The cat is my only pet.
  • class membership: (definite-noun copula noun-phrase) Garfield is a cat.
  • class inclusion: (noun-phrase copula noun-phrase) A cat is an animal.
  • predication: (noun-phrase copula adjective) The cat is furry.
  • ownership: (noun-phrase copula possessive-noun) The cat is theirs.
  • auxiliary: (noun-phrase copula verb-phrase) The cat is sleeping / The cat is being bitten by the dog
  • existence: (medial-proadverb-of-location copula noun-phrase) There is a cat.
  • location: (noun-phrase copula location-phrase) The cat is nowhere to be found.

The Wictionary Post has 23 unique uses of 'to be' in English I should read through!