Arguing a fortiori

Date01 March 2017
DOIhttp://doi.org/10.1111/1468-2230.12252
Published date01 March 2017
AuthorLuís Duarte d'Almeida
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Arguing a fortiori
Lu´
ıs Duarte d’Almeida
Courts and lawyers often argue a fortiori. Sometimes they actually use the Latin phrase to indicate
that their conclusions do not just follow, but ‘follow a fortiori’ from certain premises. These are
taken to be inferences of a distinct and important kind. But how exactly are they distinct, and
why are they important? Despite their popularity, a fortiori arguments are not well understood
and have not drawn much attention from legal theorists. This paper pursues two goals. The
first is to bring out the form of a fortior i arguments, articulating those assumptions that, though
typically left unstated, are necessary elements of arguments of this kind. The second goal is to
say something about the point of such arguments, and to characterise the sort of context in
which an arguer will have reason to deploy an a fortiori rather than an inference of a different
type.
INTRODUCTION
Courts and lawyers often argue a fortiori. Sometimes they actually use the
Latin phrase to indicate that their conclusions do not just follow, but ‘follow
a fortiori’ from certain premises. These are taken to be inferences of a distinct
and important kind. But how exactly are they distinct, and why are they
important? That is less clear. Despite their popularity, a fortiori arguments are
not well understood and have not drawn much attention from legal theorists.
I try in this paper to make some progress on the topic. I will be pursuing
two goals. The first is to bring out the form of a fortior i arguments, articulating
those assumptions that, though typically left unstated, are necessary elements
of arguments of this kind. That will be the object of the first four sections.
The second goal is to say something about the point of such arguments, and to
characterise the sort of context in which an arguer will have reason to deploy
an a fortiori rather than an inference of a different type. That will be my task in
the fifth and last section.
The first three sections are dedicated to identifying several features that
lawyers will, I think, recognise upon reflection as the key components of the
a fortiori. I will therefore be relying on my readers’ pre-theoretical familiarity
with such arguments: that is precisely what will enable them to evaluate the
soundness of my proposed account. I will also rely on readers’ ability to know
an a fortiori argument when they see it. For courts do occasionally misuse the
a fortiori’ label in connection with arguments of other kinds; and genuine
Reader in Jurisprudence, University of Edinburgh. For helpful comments and discussion, I am
grateful to Euan MacDonald, F´
abio Perin Shecaira, Frederick Wilmot-Smith, Giovanni Damele,
Lucas Miotto, Martin Kelly, Pedro M´
urias, and Hugo R. Zuleta; to the Edinburgh Legal Theory
Research Group; to audiences in Oxford and Lisbon; and to the two anonymous reviewers for The
Modern Law Review.
C2017 The Author.The Moder n Law Review C2017 The Modern Law Review Limited. (2017) 80(2) MLR 202–237
Published by John Wiley& Sons Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA
Lu´
ıs Duarte d’Almeida
instances of the argument do not need, of course, to come explicitly marked
or classified in any way.
So, for example, I take it that you will agree that Lord Kerr in Moohan
and another vThe Lord Advocate1was offering an a fortiori argument (among
other considerations) in support of his view that Article 3P1 of the European
Convention on Human Rights was applicable to the Scottish independence
referendum. This article imposes an obligation on states to hold elections ‘under
conditions which will ensure the free expression of the opinion of the people
in the choice of the legislature.’ Lord Kerr writes:
This phrasing [of Article 3P1] may, on one view, point to a focus on legislative
elections, but it by no means justifies an exclusion of other votes. Why should it?
If voting for a representative in a legislature is deemed sufficiently important that it
should be guaranteed to all, why would voting for the form of government be deemed
less important?2
This is a good example of an a fortiori argument, and I will say more about
it in the fourth section of this paper. By contrast, the following passage, from
Yearworth and others vNorth Bristol NHS Trust,3is not—the Court of Appeal’s
own claim notwithstanding—an instance of an a fortiori argument:
Had we reached the conclusion that the law in respect of parts or products of a
living human body precluded our holding that the men had ownership of sperm
for the purposes of their claims in the tort of negligence, it would clearly have
been important for us to proceed to inquire whether nevertheless they had such
lesser rights in relation to it as would render them capable of having been bailors
of it. Our conclusion that the men had ownership of it for the purposes of their
claims in tort obviates the need for that particular inquiry: for from that conclusion
it follows a fortiori that the men had sufficient rights in relation to it as to render
them capable of having been bailors of it.4
If someone has ownership of a thing, then he does have sufficient rights as
to render him capable of having been bailor of it. So the court’s conclusion
follows—just not a fortiori. It is simply that ownership is a bundle of normative
positions that contains those latter rights as a sub-class.
Scholars too sometimes give confused examples. David Daube points out
that certain kinds of argument that courts typically use—including arguments a
fortiori—are not the exclusive provinceof lawyers; they are also used in everyday
argumentation:
[T]ake as illustration the inference a fortiori—to be sure, any layman might reason
thus: ‘Here is a teetotaller who does not touch cider; he will certainly refuse
whisky.’5
2ibid at [65].
4ibid at [47].
5 D. Daube, ‘Rabbinic Methods of Interpretation and Hellenistic Rhetoric’ (1949) 22 Hebrew
Union College Annual 239, 254.
C2017 The Author. The Modern Law Review C2017 The Modern Law Review Limited.
(2017) 80(2) MLR 202–237 203
Arguing a fortiori
But this is not a good illustration. The putative a fortiori inference would rely
on the fact that the teetotaller does not touch cider, to infer that he will refuse
whisky. Yet if we know that he is a teetotaller, then the fact that he does
not touch cider plays no role in the argument: if he is a teetotaller, then it
already follows that he will certainly refuse whisky. A better illustration would
be simply this:
He does not touch cider; he will certainly refuse whisky.
Daube is right, though, that a fortiori arguments are just as usual and natural
outside the law as they are among lawyers. There is nothing specifically legal
about this type of inference, regardless of what some authors suggest.6And
perhaps it will be helpful to adopt Daube’s (revised) illustration as a working
example as we begin to make progress in understanding how these inferences
actually work. We will come back, of course, to real instances of the legal a
fortiori—in the third and especially in the fourth section, when the preceding
conclusions will be tested against several examples from judicial decisions.
But the cider-and-whisky argument—stripped of any reference, explicit or
implicit, to teetotallers—is a good specimen to tackle at first, precisely because
it is an everyday example. It is easy to grasp, and free of legal jargon and
distracting technicalities. So let us start by trying to identify its elements and
structure.
THE ELEMENTS OF THE A FORTIORI
The first thing to note is that in arguing ‘He does not touch cider; he will
certainly refuse whisky’ we will be comparing two things—cider and whisky—
and inferring, on the basis that he (our fr iend, say) will (or would) not drink the
former, that he will also not drink the latter. Why exactly not? The argument
as expressed is silent about that. But we will only understand the inference if
we grasp the point of the comparison. Suppose, then, that the context in which
the argument is being put forward makes clear that the comparison concerns
the alcohol content of the two kinds of beverage, and more specifically the fact
that cider is lower in alcohol content than whisky. And the thought behind the
argument as expressed would seem to be this: if cider, lower in alcohol content
as it is, is nevertheless already so high in alcohol content that our friend would
refuse it—if it is already too high in alcohol content for our friend to accept
it—then surely whisky too is high enough in alcohol content that our friend
would refuse it.
In order to begin to make sense of the argument, then, we have to track and
bring out an assumption which we take the arguer to be relying upon regarding
the reason why our friend will—or so the arguer claims—refuse whisky. The
assumption is that the friend’s refusal is due to the beverage’s alcohol content.
6 Klug classifies the a fortiori as one of the ‘special arguments of legal logic’ (‘spezielle Argumente
der juristischen Logik’). See U. Klug, Juristische Logik (Berlin: Springer, 4th ed, 1982) 109.
204 C2017 The Author. The Modern Law Review C2017 The Modern Law Review Limited.
(2017) 80(2) MLR 202–237

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