THE CONCEPT OF COHERENCE IN AUSTRALIAN PRIVATE LAW.

• Date: 01 April 2018
• Author: Fell, Andrew

Contents I Introduction II Coherence Generally III Coherence in Australian Law IV Coherence as Consistency A Examples of Consistency-Based Reasoning 1 Sullivan v Moody 2 Miller v Miller 3 Equuscorp v Haxton 4 Apotex v Sanofi-Aventis B What Conception of 'Consistency'? 1 Consistency in the Operation of Rules? 2 Stultification 3 Alignment between Rules and Their Reasons? V A Closer Look at Reasons and Consistency I Introduction

The concept of 'coherence' is a fundamental principle in Australian law. (1) It has been relied on by the High Court in statutory and constitutional interpretation, (2) but is relied on most often in the development and application of the common law. In that context, which will be the focus of this article, there are many cases in which the importance of 'coherence' within the common law, and also between the common law and statute law, has been acknowledged. (3) In those cases, it is generally regarded as a conclusive reason against a proposed ruling or decision that it would give rise to incoherence. (4) 'Coherence' has even been described as 'the central policy consideration' in determining the consequences of a plaintiff acting illegally in the circumstances giving rise to their claim. (5)

Despite its prominence, this 'aspiration' towards '[c]oherence within and between the common law and the statute law' is 'under-defined and understudied', as Chief Justice Robert French suggested in 2015. (6) The High Court itself has not fully articulated what it means by 'coherence', (7) and has said little about why it is important. Although some commentators have sought to elucidate the Court's approach, (8) it is generally not well understood. At a general level, the Court indicated in Miller v Miller that a 'lack of coherence' involves some kind of 'incongruity', 'contrariety' or 'inconsistency' between legal rules. (9) But it did not explain the nature of this inconsistency in great detail, although it is clear that when statutory rules are concerned, their purpose is relevant in identifying it. (10) Subsequently, in Equuscorp v Haxton, 'the objective of maintaining coherence in the law' was equated with 'the negative goal of avoiding self-stultification in the law'. (11) This was a reference to the notion of 'stultification' relied on by the late Professor Peter Birks, who suggested that it provided the basis of the illegality defence in the law of unjust enrichment. (12) Beyond this, the concept of 'coherence' or 'consistency' has not been explained. Complicating all this is that there are references to 'coherence' that clearly do not relate to the notion of consistency in the law.

If the High Court is going to rely on the 'coherence of the law' (understood as referring to some kind of consistency) in its decision-making, it is necessary to identify at least what the Court means, and the possible justificatory arguments that might support its approach. This is especially given the likelihood that coherence will become increasingly relevant in Australian legal adjudication. In contrast to past legislative practices, Grantham and Jensen note that modern legislation, when entering into common law fields, tends to establish comprehensive legal regimes that are intended to replace substantial parts of the common law but without codifying private law as a whole. In some areas, statutes therefore 'exist side-by-side with remnants of the common law. (13) As Barker points out, the resulting increase in overlap between common law and statutory norms is attended by an increased risk of contradiction between them. (14) Given that '[m]essy patterns of gradual, legislative accretion seem more likely than grand codification covering large fields', he suggests that a proper understanding of the norms relating to 'incompatibility' between common law and statute is all the more important. (15)

But 'coherence' is not only relevant to the interaction between statute and common law. As Barker also observes, the novel applications of the (potentially expansive) principles of negligence and unjust enrichment, among other examples, highlight the potential for increasing overlap and contradiction purely within the common law. Australian courts rely on various 'secondorder' principles, often in the name of 'coherence', (16) in order to prevent such conflicts between norms of different categories. There is, in his view, 'an increasing need to research, review and rationalise the operation of these second-order principles as the complexity of the system continues to increase. (17) A useful starting point in this process is to identify and examine the kind of inconsistency that these more specific principles have been tailored to avoid.

The bulk of this article will be concerned with elucidating the concept of 'coherence', as used by the High Court in the development and application of the common law. In order to facilitate this discussion, I will provide a brief overview of the possible meanings of 'coherence' in Part II. Part III will consider its meaning in decisions of the High Court. There is a variety of such meanings, but on most occasions the High Court is referring to some kind of 'consistency' in the law. I will argue in Part IV that when used in this way, the High Court can be understood as referring to consistency in the law's underlying normative reasons. This kind of consistency will be explained in more detail in Part V, drawing on philosophical literature on the theory of reasons and Ronald Dworkin's writing on 'political integrity'. Returning to a more general level, Part VI then identifies some possible arguments that might support the reliance on 'coherence in the law' in common law reasoning.

II Coherence Generally

The word 'coherent' is part of ordinary language. It is also a concept that is used in specialised academic disciplines other than law. (18) But mostly, it is left undefined or vague. (19) For the purpose of clarity, it is worth pausing to provide an overview of its possible meanings before turning to the decisions of the High Court. Raz has suggested that '[w]hat is incoherent is unintelligible, because it is self-contradictory, fragmented, disjointed. What is coherent is intelligible, makes sense, is well-expressed, with all its bits hanging together.' (20) However, these different phrases are not perfectly synonymous with one another; the notion of 'unintelligibility' is conceptually distinct from that of 'self-contradiction', which is again different from 'fragmentation' and 'disjointedness'. These differences are often overlooked. At least three distinct meanings of the word 'coherent' can be discerned in Raz's statement. The first is 'intelligible', which means something like 'capable of being understood or comprehended'. Secondly, similarly to the phrase 'makes sense', it can also mean something like 'sound' or 'based on good reasons. (21) Thirdly, as a relation between things or parts of a thing, it can mean 'without contradiction or inconsistency'. Later, Raz also equated coherence and 'unity', (22) and this meaning can be added to the first three. This final meaning is also reflected in Raz's explaining of 'incoherence' in terms of fragmentation and disjointedness. It conveys the notion of being joined together (not necessarily in a physical sense), and of singularity.

Although these meanings refer to conceptually distinct properties, 'coherence' of one kind can contribute to coherence of another. A set of random words is not capable of being comprehended because it lacks unity. A novel that is riddled with inconsistencies might be difficult to understand or follow. The operation and interaction of the various parts of a legislative scheme might be difficult to identify and comprehend if it does not reflect a sound and unified normative policy. There are no doubt other examples. The main point to note for present purposes is that this multiplicity of closely interrelated meanings undoubtedly contributes to a lack of precision in using and interpreting the concept. Bearing this range of possible meanings in mind will assist in understanding the decisions of the High Court.

III Coherence in Australian Law

The context in which the High Court most frequently refers to 'coherence' is in describing, developing and applying the common law. In that context, a variety of meanings can be discerned, which generally map to those identified in the previous section. Consider the recent decision in Prince Alfred College v ADC. (23) In that case, the majority observed that '[c]ommon law courts have struggled to identify a coherent basis for identifying the circumstances in which an employer should be held vicariously liable for negligent acts of an employee'. (24) There are several indications of what the word 'coherent' might mean here. Firstly, the heading immediately preceding the paragraph in which the statement appears questions whether there is a 'general basis' for vicarious liability. The majority also noted that a 'general principle' has 'eluded the common law for a long time'. (25) Secondly, the majority suggested that a general principle might provide certainty, but that one partly based an exercise of judgment of what is 'fair and just' (like that utilised in the UK) would involve policy choices, on which minds may differ. (26) Such an approach would also 'not proceed on any principled basis or by reference to previous decisions'. (27) Finally, repeating comments in an earlier decision, the majority observed that 'a "fully satisfactory rationale for the imposition of vicarious liability" has been "slow to appear in the case law'". (28)

Considering this, the majority, in referring to a 'coherent' basis for imposing vicarious liability, could variously be understood as referring to one which is general, certain in its application, non-discretionary, or based on a satisfactory normative rationale. The reference to generality can be seen as connected with the concept of...