Sources of legal indeterminacy

• DOI: https://doi.org/10.47348/SALJ/v138/i1a6
• Pages: 115-151
• Published date: 04 March 2021
• Date: 04 March 2021
• Citation: 2021S (1) SALJ 115
• Author: Du Plessis, Q.

115

SOURCES OF LEGAL INDETERMINACY

*

QUENTIN DU PLESSIS†

Johannesburg Bar

Traditional analyses characterise or identify vagueness and ambiguity as the sole or

primary sources of legal indeterminacy. In this article, I identify and characterise

various other sou rces of legal indetermina cy. In addition to the semantic indeter minacy

of vagueness and ambiguity, philosophers of language have identied conversational,

pragmatic, and contextual indeterminacy, each of which is capable of generating a

‘hard case’ as applied to the legal sphere. Nor is all legal indeterminacy linguistic in

nature. Followin g Henry Prakken, I identify non -monotonicity, or the fact that legal

inferences are defeasible, as a nal source of legal indeterminacy. Each source of legal

indetermina cy thus identied includes case-law examples to aid in the discussion.

Legal indeterminacy – semantics – vagueness – ambigu ity – interpretation

– context

‘Look for precision in each class of things just so far as the nature of the

subject adm its.’1

I INTRODUCTION

Law is not like m athematics or physics. It does not cons ist of the application

of abstract principles to concrete scenarios to yield uniquely true answers.

Every legal system has legal obligations and rights, the precise content of

which is indeterminate. Indeterminate legal norms generate hard cases in

their penumbra of application. The distinguishing feature of hard cases

is that no decision procedure considering only the dictates of law could

tell one what the outcome will be. To the extent that certain legal norms

generate hard cases, they pose an immediate and obvious challenge to the

rule of law. If we take the point of the rule of law to be the guidance of

legal subjects, then such norms are a failure, since they cannot guide our

behaviour, since we cannot know what counts as a violation of them.

All legal norms a re indeterminate to a g reater or lesser extent. No legal

norm is perfectly determinate. We can measure the indeterminacy of a

legal norm by t he relative size of the set of hard ca ses to the set of easy cases

that it could possibly generate. For instance, s 10 of the Constitution of

the Republic of South Africa, 1996 (‘the Constitution’), which states that

‘[e]veryone has inherent dignity and the right to have their dignity

* This article is based substantially on ch 2 of my LLM dissertation which,

in turn, owes much to ch 1 (‘Forms of legal indeterminacy’) of David Lanius

Strategic Indeterminacy in the Law (2019). Many thanks go to Lanius for allowing

me to stand on his shoulders. Thanks go also to my supervisor, Professor Anton

Fagan, for incisive comments during the wr iting of the draft. Any errors remain

mine alone.

† BSocSc LLB LLM (Cape Town).

1 Aristotle Nicomachean Ethics (tr W D Ross) (1942) I iii 1094b.

https://doi.org/10.47348/SALJ/v138/i1a6

(2021) 138 SALJ 115

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116(2021) 138 TH E SOUTH AFRICA N LAW JOURNAL

https://doi.org/10.47348/SALJ/v138/i1a6

respected and protected’,2 is extremely indeterminate,3 since the set of

hard case s that it could generate is arguably larger than the set of easy case s

that it could generate.4

Thus understood, indeterminacy is a modal notion.5 One consequence

is that a lega l norm is actual ly indeterminat e only relative to some context.

Section 10 of the Constitution is perfectly determinate as applied to

the context of a legal subject purporting to stand in the relationship of

ownership to a nother legal subject. Thi s would be a clear case of a violat ion

of s 10. Similarly, s 10 is perfectly determinate as applied to the context

of a legal subject purporting to stand in the relationship of ownership to

a legal object. This is a clear case of non-violation of s 10. Even the most

indeterminate legal norms are thus actually determinate when applied to

an appropriate context.

The extent to which a leg al norm succeeds i n guiding t he behaviour of its

subjects wi ll depend on its indeterm inacy. Completely indeterm inate legal

norms fail completely to guide our behaviour since there is, ex hypothesi,

no context in which it is c lear whether they apply. Less indeterm inate legal

norms guide our behaviour only relative to some context. If, relative to

some context, an i ndeterminate le gal norm generate s an easy case, then t hat

norm will succeed in guiding our behaviour. If, relative to some context,

an indeter minate legal norm g enerates a hard case, then t hat norm will fa il

in guiding our behaviour. Completely determinate legal norms should,

ceteris paribus, succeed completely in guiding our behaviour.

One way to thin k about the dierence between law and mathematics is

that, un like mathematics , the legal system does not v alidate the princ iple of

bivalence. In logic, the principle of bivalence states that every proposition

2 The Constitution, s 10.

3 Both Deeksha Bhana and Gerhard Lubbe argue in eect that dignity is

multidi mensional in that it i ncorporates both ‘empower ment’ and the notion that

humans should not be treated as the means to an end. See Deeksha Bhana ‘The

law of contract a nd the Constitution’ (20 07) 124 SALJ 269 at 274; Gerhard Lubbe

‘Taking fundamental rights seriously: The Bill of Rights and its implications

for the development of contract law’ (2004) 121 SALJ 395 at 420–1. Dignity,

according to Lubbe (at 421), can pull in opposite directions. See also Jan Smits

‘Private law and fundamental rights: A sceptical view’ in Tom Barkhuysen &

Siewert Lindenbergh (eds) Constitutionalisation of Private Law (2006) 9 at 17 and

F D J Brand ‘The role of good faith, equity and fairness in the South African

law of contract: The inuence of the common law and the Constitution’ (2009)

126 SALJ 71 at 86: ‘[Dignit y is] simply too vague to provide a decisive an swer in

deciding cases.’

4 For this rea son, callin g these cases ‘penumbra l’ or ‘borderli ne’ is a misnomer

as applied to ex tremely indeterminate legal norms.

5 Modal propositions are propositions subject to either of the sentential

operators ‘it is possible that’ or ‘it is necessary that’ (as opposed to ‘it is actually

the case that’). In the sense u sed here, to say that a proposition p is indeterminate

is equivalent to ‘it is possible that p could generate a hard case’.

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has one and only one truth value: true or false. The set of all propositions

would then be divided equally between two mutually exclusive and

exhaustive subsets: the set of all true propositions and the set of all false

propositions. In law, juridical bivalence would entail that every legal

proposition is either true or false, and not both, and not neither. Thus,

everyperson either is or is not guilt y; every actioneither does or does not

constitute a delict; and every agreement either is or is not unlawful.

Despite this being the layperson’s view of the law, it is false. The reason

is legal indeterminacy. This article aims to identify, in a sort of taxonomy

of legal indeterminacy, some of the most pertinent ways that juridical

bivalence can fail. I have already identied, on the most general level,

one way in which it can fail: two mutually exclusive legal utterances are

not always mutually exhaustive of the legal space. There are several ways

in which this can happen, but most scholars focus on just two: vagueness

and ambiguity.

In this article, I propose a modication and extension of Lanius’s

taxonomy of ways that juridical bivalence can fail.6 According to this

classi catory scheme, vagueness and ambiguity are mere species amongst

genera. I attempt, further, to make the discussion of each source of legal

indeterminacy concrete by discussing case law examples of each.

The article is organised as follows. Part II is dedicated to an

exploration of semantic indeterminacy, which includes vagueness and

ambiguity. Vagueness can further be distinguished between its soritical

and combinatorial manifestations, and ambiguity between its syntactic,

lexical, and polysemous manifestations. Part III concerns conversational

vagueness, which occurs when an utterance borderline satises a

Gricean conversational maxim, the most common example of which is

generality. Part IV is concerned with pragmatic indeterminacy, which

occurs when a proposition that is semantically determinate nonetheless

generates indeterminacy due to pragmatic considerations surrounding the

utterance. Th is includes implicat ure indetermin acy, speech-act ambiguit y,

presupposition indeterminacy, and explicature indeterminacy. Part V

looks at indeterminacy in context, which is concerned with the problem

of context-determination.

Part VI considers a wholly dierent source of legal indeterminacy,

which is due not to two mutually exclusive legal utterances not being

mutually exhaustive of the legal space, but due rather to the fact that the

truth of one of a set of two mutually exhaustive legal utterances does not

guarantee the falsity of the other. Here, I focus on the non-monotonicity

of legal reasoning, which is to say that all legal propositions are, at least in

principle, defeasible. Part VII concludes the article.

6 See David Lanius ‘Forms of indeterminacy’ in his Strategic Indeterminacy in

the Law (2 019) 4– 61.

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