Excerpt:

Forgive the oxymoron, but how do you define vagueness?

A vague concept allows borderline cases. The potential confusion is that people think vagueness is when they don’t quite get what someone means.

For people in my area of logic, it’s actually a much narrower phenomenon, such as the word “grey”. Some birds are clearly grey, some are clearly not, while others are somewhere in between. The fact that such birds exist makes “grey” a vague concept. The vagueness does not arise from insufficient information: some concepts are fundamentally vague.

On the other hand, if I say that I have fewer than three children, that’s not vague. In fact, it is the opposite, it is “crisp”. It is true if I have zero, one or two children, and it is false if I have three or more.

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