During a presidential forum in the 2008 US presidential campaign, the moderator, Pastor Rick Warren, wanted Senator John McCain and then-Senator Barack Obama to definerichwith a specific number. Warren wanted to know at what specific income level a person goes from being not rich to rich. The problem with this question is that there is no specific income at which a person makes the leap from being not rich to being rich. This is becauserichis a fuzzy set, not a crisp set, with different incomes having different degrees of membership in therichfuzzy set. Fuzzy logic is needed to properly ask and answer Warren's question about quantitatively definingrich. An imprecise natural language word likerichshould be considered to havequalitative definitions, crisp quantitative definitions,andfuzzy quantitative definitions.
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