You know what else isn't an abstract concept?
Being 'cool'...'coolness'.
Beauty is an abstract concept, but being cool isn't and we all know who the cool ones are don't we because we're told every day who's cool and who's not.
We're also told what's moderrn and not modern because being modern isn't an abstract concept.
See below for official definitions.
Cool
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Not Modern
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Abstract Concept (ugly to some)
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