The quality of being attainable; the degree to which something can be achieved or reached.
From 'attainable' plus the suffix '-ness,' which creates abstract nouns from adjectives. This formation follows standard English word-building patterns but is relatively rare in modern usage, which prefers 'attainability.'
English has two ways to say basically the same thing—'attainability' and 'attainableness'—and the first one is winning out, showing how modern English prefers Latin-based suffixes ('-ity') over Germanic-based ones ('-ness') in abstract terminology.
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