From June 17 to 27, 2025 the ALF Summer School on Logical Reasoning and Law took place in Lisbon. During this event, I gave a talk entitled ‘Legal logic(s): one or many? And what are they for?’.
The starting points of the talk were the following:
(1) There is more than one system of logic.
(2) There is also more than one system of legal logic.
Against this background, I argued that
(3) How the basic building blocks of law are conceptualised influences the logic of law and vice-versa.
If different legal logics and different conceptualisations of the basic building blocks of law are possible, this raises the question how one should choose between the different possibilities or evaluate their merit. Here, I suggest that
(4) Proximity to usage as well as clarity and consistency are relevant criteria, but that the ultimate criterion is coherence between the purpose for which the logic and conceptualisations of the basic building blocks are intended (e.g. a descriptive or a critical research project), the values assigned to proximity to usage, clarity, and many other epistemological and ontological commitments.
The talk was meant to provide guidance to (young) scholars faced with different systems of legal logic and the choice between them. I will not here reproduce the argument of the talk at length.
Instead, I want to point to the following: each of the numbered items above relies heavily on (implicit) ontological and epistemological background commitments. Of course, each of these starting points or claims deserves to be elaborated upon far beyond what I did in the talk (and will do in the publication to follow), and each of them can (and has) been debated. Underlying those debates are different (metaphysical) commitments.
The first starting point, for example, that (1) there is more than one system of logic, for example, is not obvious. In this connection, I find the threefold distinction by Susan Haack between logical monism, logical pluralism, and instrumentalism helpful (Haack 1978: 221-242). Logical monism is the position that there is only one correct system of logic; logical pluralism is the position that there are multiple correct systems of logic; instrumentalism is the position that ‘correct’ is not the correct determinant. Correctness can be system-relative (something is a valid argument relative to a system of logic) or refer to truth or validity that is external to the system of logic in question. While it is clearly the case that different scholars of logical reasoning and law have put forward different proposals of legal logic, the monist would hold that only one of them is correct – if indeed there is such a thing as legal logic as distinct from general logic at all, which the monist would also deny. The step from logic to legal logic already presupposes pluralism, at least between domains, if legal logic is something distinct from logic tout court. This, too, can be questioned – and indeed, in his Introduction to Legal Reasoning that also formed part of the summer school, Miodrag Jovanovic addressed this question. If we accept that law as a domain needs its own logic, this does not settle the debate. Within the domain of law, is there one correct system of logic, many correct systems of logic, or is ‘correct’ the wrong term here and the merit of one system of logic over another does not depend on its extra-systematic truth or validity, but for example on usefulness?
I will not – and indeed, cannot – answer that question here, but I want to point out that reflecting even on the starting points of my talk already leads to metaphysical reflections, ranging from whether a system of logic is the kind of thing that can be assessed as true or false, what notion of truth determines extra-systematic validity of a logical system, if any at all, and more.
The nature of law is similarly debated (Atiq, Marmor, Sarch 2025), as is the question how to conceive of the building blocks of law. What is a norm, for example, and are different conceptions of ‘norm’ possible and can they be equally correct? Is ‘correct’ even the best determinant? Bix has argued that conceptual claims are not right or wrong, but that their merits depend on the purpose for which they are made (Bix 1995: 467).
Some might argue that conceptual definitions can only be arbitrary, because there cannot be any one right way to divide up social reality. For example, one might argue that regarding questions like whether we describe the rules of wicked governments as law or whether we consider international law as really being law, any answer is as true or as legitimate as any other. Under this analysis, there cannot be a “right” or “wrong” to conceptual definitions, only a “more or less useful” or a “more or less convenient for certain purposes,” and all that we can ask is that theorists be as clear as possible […].”
He then goes on to argue that beyond arbitrary stipulation, conceptual claims can also have as their objective that they track and explain linguistic usage, that they discover the significance of a concept hidden in our practices and intuitions, or that they impose moral or qualitative criteria on when a label should be applied (Bix 1995: 471). Similarly, we might want a system of legal logic to track and explain the reasoning practices of legal officials, often but not necessarily focusing on courts in this regard, or we might want it to impose qualitative criteria on when the label ‘good legal reasoning’ should be applied. This would suggest that the merit of a system of legal logic also depends on the purpose for which it is used. But this again requires that there is no such thing as the true matter of fact about legal logic. If law and legal reasoning are part of social reality, the argument that ‘there cannot be any one right way to divide up social reality’ (Bix 1995: 470) holds sway – but whether law and legal reasoning are part of social reality is, again, debated and the answer to that question will, again, depend on ontological and epistemological commitments.
In the talk I gave at the summer school, I held that the merit of a system of legal logic (and the conceptualisations of the basic building blocks of law to go with it) depends on its coherence with, inter alia, the epistemological and ontological commitments underlying it. In this blog post, I have sought to demonstrate that the merit of the claims on which I relied during the summer school similarly depends on their coherence with, inter alia, the epistemological and ontological commitments one holds. Of course, one might still argue that I am wrong about this and that there is a truth of the matter, whether ‘the matter’ is the nature of law, legal logic, or methodological claims – but that argument, too, would rely on certain ontological and epistemological commitments that could, again, be questioned and argued.
In short: it’s coherence all the way down.
To read more about this, check out this article: Hage, Jaap, Antonia Waltermann, and Gustavo Arosemena, ‘Exceptions in International Law’, in Lorand Bartels, and Federica Paddeu (eds), Exceptions in International Law [LINK]
SUGGESTED CITATION: Waltermann, Antonia, “Choosing Legal Logic”, FOLBlog, 2025/10/15, https://fol.ius.bg.ac.rs/2025/10/15/choosing-legal-logic/