Published on December 22, 2021
Job titles and other details are as of the time of publication.
(The interview was conducted in Japanese and was thereafter translated into English.)

Research style of tracing back to principles for a wide range of fields

My area of specialization, legal philosophy, poses a famous question: Is there a moral obligation to obey an evil law?

To answer this question, we must delve into moral philosophy and ethics to understand the nature of evil; we then explore metaethics, which asks what morality is in the first place, and we have no choice but to delve even deeper into metaphysics questioning whether morality actually exists as an objective entity in the world. Inevitably, this leads us into the profundity of linguistic philosophy, which deals with the question: What are we trying to communicate when we say something is “right” or “good”?

My philosophical approach is to trace these uncontestable principles back as far as possible and begin the discussion from there. Revisiting these principles allows us to address real-world issues comprehensively and consistently, even when they appear to lie outside the domain of philosophy. In this way, I believe legal philosophers have a unique role to play in discussing a wide range of (or rather, “miscellaneous”) topics, such as AI governance, the harm of death, posthumous harm, and intergenerational justice, rather than one particular major theme.

Selecting a seminar on legal philosophy (theory of justice) after dissatisfaction with my positive law class

I became interested in law as a high school student. It was just around the time when Japan introduced its law school system, and I envisioned a career path leading from university to law school and eventually to the legal profession.

However, I was hesitant about becoming a judge or a prosecutor, having learned about their demanding nature of the work from friends whose parents practiced these professions. Judges and prosecutors face frequent relocations and numerous restrictions on their daily lives. In such a stressful environment, I doubted whether I could aptly handle court cases that would affect people’s lives profoundly. Thus, I enrolled in university believing that a career as a lawyer would suit me best.

But before starting my junior year, I was unsure if I was cut out for legal practice. I was totally discontented with my sophomore year’s positive law courses, which focused only on court cases and society during specific periods. Whenever individual cases and theories were discussed, I was dissatisfied with conclusions that cannot be drawn logically, while most students seemingly accepted them without question. At one point, the situation became unbearable; “illogical” might be an overstatement, but I could not help feeling skeptical about discussions that rely on hidden premises and visible “holes” being ignored.

I decided to enroll in a seminar course on legal philosophy in my junior year. Legal philosophy has two main research topics: one is legal theories, which examine what law is and the other, theories of justice focusing on what law ought to be. I had no hesitation choosing the seminar on the latter topic and I had been fed up with the study of positive law, though I had never expected to eventually become a legal philosopher.

No rules should be made without anticipating the consequences

My seminar advisor, Professor Tatsuo Inoue (current professor emeritus at the University of Tokyo), discussed the law and economics theory advocated by Richard Allen Posner (American legal scholar and judge of the US Court of Appeals for the Federal Circuit). At that time, I attributed my dissatisfaction with positive law to its lack of scientific rigor, and I saw economics, which strives to be a science, in a very positive light. Another reason why I chose this seminar was my expectation that linking economics to law could allow us to predict the consequences of legislation to some extent.

To enact a rule into law, we must predict people’s behaviors and rely on these outcomes to determine whether the rule should become law. I sympathized with Posner’s position that weighs the consequences and lawmakers’ responsibility, namely, the position that no rules should be enacted without a clear understanding of their potential consequences (broadly, utilitarianism).

The revision to Japan’s Act on Land and Building Leases serves as a well-known example of Posnerian law and economics. The original law aimed to protect vulnerable tenants but resulted in higher rents by increasing burdens on renters and reduced housing availability for low-income people.

Economists highlighted these unintended consequences, leading to revisions that addressed the issue of indefinite tenant occupation. This case illustrates the value of integrating economic analysis with legal policymaking.

The premise of “equals should be treated equally” that everyone can agree upon

My encounter with Professor Inoue’s book had a major influence on me as well. When I read his book titled Kyosei no Saho (Decorum of Conviviality) (awarded the Suntory Prize for Social Sciences and Humanities in 1986), I was struck to learn that justice can be discussed as an academic subject beyond simply feeling good or bad (while I now disagree with much of its arguments, I still highly recommend it for its thought-provoking insights).

The book begins with the premise that “equals should be treated equally,” a principle that serves as the core of the concept of justice. Most cases that elicit people’s reactions like "That's unfair!" stem from violations of this principle, such as favoritism or egoism. By addressing these violations, we can resolve many questions of justice without delving into substantive discussions of justice.

The book left a vivid impression and taught me something I had not learned before. It explained that justice can be rationally discussed without falling into relativism. Some may think it strange for me, a person who once was dissatisfied with the unscientific nature of legal studies, to develop an interest in philosophy (and for that matter, moral philosophy), among other topics. However, the community of analytic philosophers, of which I believe I am among the members, regards discussions that cannot proceed without ignoring the “holes” I mentioned above as unacceptable, as is often the case in legal studies (which I originally complained of). After some years of research in metaethics, I am now a proponent of naturalistic moral realism and believe that moral philosophy, including the theory of justice, can be pursued scientifically and essentially no different from natural science. Looking back, I realize that the challenges faced in my first year have strongly shaped what I am today.

The world’s discussions taking place with significant hidden premises

Discussions on justice often involve fundamental disagreements rooted in hidden premises. Such hidden premises often lead to fruitless conflicts, underscoring the importance of identifying the true points of contention.

For example, arguments between the two philosophers Robert Nozick and John Rawls were famous. On the surface, the point of contention was whether a welfare state should be rejected or defended, but this was not the case. To begin with, it was natural for two philosophers with different positions, classical libertarian Nozick and Rawls with a redistributive liberal stance, to reach incompatible conclusions. The actual source of contention between the two sides, namely, a significant hidden premise, was about whether justice should prioritize individual behavior (as Nozick argued) or social institutions (as Rawls proposed). No one but a saint would believe that egalitarian redistribution should be practiced or forced upon others in every aspect of daily life. If so, why is egalitarian redistribution (mandated by a state) considered right for a social institution? Why can the principle that cannot ground the rightness (or permissibility) of people’s individual actions ground the rightness of social institutions? This is exactly the core of the debate.

Basically, the world’s discussions, if not limited to the theory of justice, often proceed with significant hidden premises and continue in futile conflict because of them. It is no exaggeration to say that humankind has repeated such conflicts for thousands of years through the 21st century. This is why I believe the examination of hidden premises and where the true points of contention lie is invaluable training for critically studying positive law. It is not uncommon for an academic theory to rely totally on unconvincing hidden premises.

Encouraging Hitotsubashi University students to stick to policymaking that can deliver outcomes

When teaching classes concerning theories of justice at Hitotsubashi University, it is never my intention to ask students to determine which theory is correct, though they are free to do so. Instead, I encourage them to critically ask “Do the arguments make sense in the first place?” “What are the hidden premises?” and “Where do the real points of contention lie?”

In class, definitions of words are built up one by one using the method of analytic philosophy, which should not be too much work. Developing the abilities to treat arguments fairly and to identify the true points of contention is the key to acquiring the justice mindset of “equals should be treated equally.” I want students to acquire these abilities as future policymakers. It is my hope that Hitotsubashi University students who study law and economics will be committed to justice and effective policymaking without overlooking the real nature of our political conflicts and the causal consequences of policies when they begin to work.