‘The copula can be used in many different situations.’
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Also, I think you underestimate the amount of variation in other words, e.g.:
> If I say "she came from school" it is clear that we're talking about relative motion today or in the recent past from one nearby location to another.
Not just recent past, but having any time near to the point of reference: ‘When she came from school after the bomb scare…’.
> If I say "her family came from Japan" it is clear I'm talking about ancestry and/or a long ago emigration, but also spatially oriented.
Or they might have arrived yesterday to visit her.
> If I say "the party is from 3pm to 5pm" then I am using "from" to indicate a temporal rather than a spatial motion.
But only because ‘3pm’ and ‘5pm’ themselves have clear temporal reference as opposed to spatial reference. For an ambiguous example, if I say ‘we drove from breakfast to lunch’, that might mean we drove starting at breakfast-time and finishing at lunch-time, or it might mean we started at a location where we had breakfast and drove to a location where we had lunch. (To more fully show that the latter is a valid interpretation, consider ‘we drove from breakfast to breakfast’: it makes no sense if ‘breakfast’ is a time, but it makes sense if treated with the sense of ‘place where we had breakfast’.)
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> The IS-A vs HAS-A relationship is entirely different. It is the difference between existential quantification (some aspect of this thing resembles/has an X) and universal quantification (the entirety of this thing is fully captured by the meaning of X).
This doesn’t sound quite right to me. In my view, both ‘has’ and ‘is’ are basically relationships, rather than quantifiers. Consider a sentence like ‘I have the keys’: this merely states a relationship between two objects, rather than quantifying over any set. A sentence like ‘The morning star is the evening star’ is similar in this regard. It is true that a sentence like ‘I have a key’ has existential meaning — but I suspect the quantification is linked to the indefinite article ‘a’ more than the verb.
> To make this concrete, if I say "he is bad" then it is unclear whether I am saying that person is an intrinsically bad man, or if I am just commenting that the thing that he is doing right now is not morally justified.
This ambiguity isn’t limited to the copula, though. ‘I like him’ has exactly the same kind of ambiguity.
‘The copula has many uses.’
or:
‘The copula can be used in many different situations.’
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Also, I think you underestimate the amount of variation in other words, e.g.:
> If I say "she came from school" it is clear that we're talking about relative motion today or in the recent past from one nearby location to another.
Not just recent past, but having any time near to the point of reference: ‘When she came from school after the bomb scare…’.
> If I say "her family came from Japan" it is clear I'm talking about ancestry and/or a long ago emigration, but also spatially oriented.
Or they might have arrived yesterday to visit her.
> If I say "the party is from 3pm to 5pm" then I am using "from" to indicate a temporal rather than a spatial motion.
But only because ‘3pm’ and ‘5pm’ themselves have clear temporal reference as opposed to spatial reference. For an ambiguous example, if I say ‘we drove from breakfast to lunch’, that might mean we drove starting at breakfast-time and finishing at lunch-time, or it might mean we started at a location where we had breakfast and drove to a location where we had lunch. (To more fully show that the latter is a valid interpretation, consider ‘we drove from breakfast to breakfast’: it makes no sense if ‘breakfast’ is a time, but it makes sense if treated with the sense of ‘place where we had breakfast’.)
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> The IS-A vs HAS-A relationship is entirely different. It is the difference between existential quantification (some aspect of this thing resembles/has an X) and universal quantification (the entirety of this thing is fully captured by the meaning of X).
This doesn’t sound quite right to me. In my view, both ‘has’ and ‘is’ are basically relationships, rather than quantifiers. Consider a sentence like ‘I have the keys’: this merely states a relationship between two objects, rather than quantifying over any set. A sentence like ‘The morning star is the evening star’ is similar in this regard. It is true that a sentence like ‘I have a key’ has existential meaning — but I suspect the quantification is linked to the indefinite article ‘a’ more than the verb.
> To make this concrete, if I say "he is bad" then it is unclear whether I am saying that person is an intrinsically bad man, or if I am just commenting that the thing that he is doing right now is not morally justified.
This ambiguity isn’t limited to the copula, though. ‘I like him’ has exactly the same kind of ambiguity.