「架空」means 'fictional' or 'imaginary' in Japanese, but according to meanings of Kan-characters (漢字) , as 架 ＝ bridge and 空 ＝ gap ( or empty ) ,
in some sense the word 「架空」implicates that a bridge as a gauge is put on a gap to roughly measure the span of it between this side and another side ( or a real part and an imaginary part ).
Accordingly, 「架空の」processes must be provisionally ( or hypothetically ) repeated to catch a more precise interval.
