Koten shisho' are not the so-called super-ancient documents (koshi koden) but instead four representative and basic literature were picked from the usual 'Shinto scriptures,' and therefore it is just another term for 'Shinto scriptures.'
「古典四書」はいわゆる超古代文書（古史古伝）ではなく、通常の「神典」から代表的・基本的な四書を出したもので、実質は「神典」の言い替えにすぎない。