Luhmann never underlined sentences in the text he read or wrote comments in the margins. All he did was take brief notes about the ideas that caught his attention in a text on a separate piece of paper: “I make a note with the bibliographic details. On the backside I would write ‘on page x is this, on page y is that,’ and then it goes into the bibliographic slip-box where I collect everything I read.” (Hagen, 1997)
