The subject of the book is the examination of "gaps in the law." Elze focuses exclusively on positive law, particularly modern private law. He divides his treatise into two main points: the "gap" and the "filling of the gap." First, Elze defines the "gap" as a term in common language and in law. He discusses components of the legal system, the "incompleteness" that would result in a gap in the law, and the resulting unintended consequences, which he then defines in terms of legally relevant facts according to non-statutory law and law tolerated by the statute. In the second main point, Elze addresses the "filling of the gap." He defines the nature and the person of the gap-filler and concludes his treatise with considerations on the identification of the law that fills the gap.