During his impeachment scandal, Bill Clinton infamously said, “It depends upon what the meaning of ‘is’ is.” Saying so was likely not very politically astute and it seems to have been irrelevant at the time. However, he was onto something interesting. So, what is the meaning of the English verb “to be”?
Here are some data to help you out. All of these use “to be” in various ways.
- Joan is nice.
- A screwdriver is vodka and orange juice.
- Justin Trudeau is a Liberal.
- Cats are mammals.
- Batman is Bruce Wayne.
- I think, therefore I am.
- Water is H2O
Fields you may wish to think about to help through this question and define the concept of “to be”: set theory, formal logic proper, comparative linguistics, and languages other than English. A little hint to avoid bending your brain too much: consider #7 last.
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As far as one can tell from Keith’s examples, there exists no precision to the use of the verb “to be” in English. As used, it denotes some form of equivalence, but it varies widely in application. As for the last example, “Water is H2O”, the power of the verb “to be” appears reduced down to simply describing “water” as sometimes denoted by a certain symbol.
It might be helpful to think about it as having multiple uses, rather than trying to shoehorn all the different uses into a single definition.
You could say “is” is:
1. defining identity, saying the two things on either side of the “is” are the same thing:
** “A screwdriver is vodka and orange juice.”
** “Batman is Bruce Wayne.”
2. describing a subset relationship, saying something is a member of some group, or an instance of some abstract:
** “Justin Trudeau is a Liberal.”
** “Cats are mammals.”
3. describing something in terms of a trait or property that it has:
** “Joan is nice.”
** “Water is H2O”
4. asserting existence:
** “I think, therefore I am.”
Any use of “is” is doing one of those things. To figure out which, you can try replacing “is” with something more precise. Examples might be:
1. “equals” (or just leave this as “is”):
** “A screwdriver equals vodka and orange juice.”
** “Batman equals Bruce Wayne.”
2. “is an example/instance of”:
** “Justin Trudeau is an example/instance of a Liberal.”
** “Cats are examples/instances of mammals.”
3. “has the property {property} =”:
** “Joan has the property {personality} = nice.”
** “Water has the property {molecular formular} = H2O”
4. “exists”:
** “I think, therefore I exist.”
There will be situations where it’s not clear which case it is (is “a screwdriver is vodka and orange juice” a case of identity/definition/’equals’, or is it a case of ‘has the property {ingredients} =’), and where the context could change the case (are you defining what a screwdriver is, or describing what it is made of). If the distinction matters, the speaker will probably use more explicit language.
Or not. People often speak vaguely, assuming you’re on the page. They’re usually right, but not always.