Impractical theory; arguments or reasoning that ignore practical realities and are unlikely to work in practice.
会議は専門用語ばかりで、結局は空理空論に終始した。
The meeting was full of technical terms and ultimately consisted of impractical theory.
現場を見ずに判断するのは空理空論に過ぎない。
Making decisions without seeing the field is nothing more than impractical theorizing.
彼の提案は理屈は立つが、現実には空理空論だ。
His proposal is logical, but in reality it's just impractical theory.