  This makes it worthwhile to proceed in the other direction and start with the hypothetical concept of consequence, i.e., characterize consequence directly without reducing it to the categorical case. Philosophically this means that the categorical concept is a limiting concept of the hypothetical one. In the classical case, truth would be a limiting case of consequence, namely consequence without hypotheses. This program is closely related to the approach of categorial proof theory (section 2.5), which is based on the primacy of hypothetical entities (“arrows”). Formally, it would give preference to the sequent calculus over natural deduction, since the sequent calculus  allows the manipulation of the assumption side of a sequence by means of left-introduction rules. 