The Dual‐Nature Thesis: Which Dualism?

• Published date: 01 September 2020
• DOI: http://doi.org/10.1111/raju.12295
• Author: Jan‐Reinard Sieckmann
• Date: 01 September 2020

© 2020 The Authors. Ratio Juris published by University of Bologna and John Wiley & Sons Ltd.

Ratio Juris. Vol. 33 No. 3 September 2020 (271–282)

The Dual-Nature Thesis:

Which Dualism?

JAN-REINARD SIECKMANN

Abstract. According to Robert Alexy’s dual-nature thesis, “law necessarily comprises both a

real or factual dimension and an ideal or critical one.” I will suggest, first, that various dualisms

need to be distinguished, in particular the empirical and the normative, the real and the ideal,

the formal (procedural) and the substantive; second, that the dualism of the empirical and the

normative and, within the latter, of the real and the ideal “ought,” is not specific to law but per-

tains to any normative system; and, third, that a dualism that distinguishes law from morality

is a dualism of formal and substantive principles, which also serves to explain the authoritative

character of law.

1. Introduction

Robert Alexy’s thesis of the dual nature of law states “that law necessarily comprises

both a real or factual dimension and an ideal or critical one” (Alexy 2010, 167). This

is, according to Alexy, “the single most essential feature of law” (ibid., 180). However,

I will argue that the dual-nature thesis is ambiguous and needs clarification. In

particular:

First, various dualisms must be distinguished, in particular, the empirical and the

normative, the real and the ideal, the formal (procedural) and the substantive.

Second, the dualism of the empirical and the normative and, within the latter, of

the real and the ideal “ought,” is not specific to law but pertinent to any normative

system and, therefore, not sufficient to present a most essential feature of law.

Third, a dualism that distinguishes law from morality is that of formal and sub-

stantive principles. This dualism may be regarded as the most essential feature of

law, explaining its authoritative character.

2. The Dual-Nature Thesis

In its most abstract form, the dual-nature thesis claims that law has both a real

and an ideal dimension. The real dimension of law is represented by the elements

of authoritative issuance and social efficacy; the ideal dimension, by the element

of moral correctness (Alexy 2002a, 13; 2010, 167). The element of moral correct-

ness makes the concept of law nonpositivistic. In order to arrive at concrete con-

tent and a clear structure, Alexy purports to explicate the dual-nature thesis in a

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