noun, noun which may take the genitive case particle 'no'
abstract theory; impractical theory; empty theory
Refers to a theory or argument that is detached from reality and cannot be put into practice. Often carries a negative nuance of being unrealistic or useless.
彼の提案は空論に過ぎない。
His proposal is nothing more than an impractical theory.
その計画は空論で終わった。
The plan ended up as an empty theory.
Compound of 空 (くう, 'empty, sky') and 論 (ろん, 'argument, theory'). The exact historical derivation is uncertain, but the combination straightforwardly conveys 'empty theory'.