As rector of Leiden University, I am sometimes buttonholed by concerned individuals on Twitter, at alumni events and even at the local market about some recent controversial statement that one of our scholars has made in the media.

These individuals are typically embarrassed by the comments, and ask me what I?am going to do about them. But asking university leaders to silence their professors strikes me as perverse. Leiden has for centuries had as its motto ¡°Praesidium Libertatis¡± (¡°Bastion of Freedom¡±), symbolising the courage to speak truth to power. Diversity of opinion is a core principle for us ¨C and for universities in general, which, more than any other institution, must maintain a commitment to defending the freedom of the spoken and written word. Our institution must always be a safe haven where all questions can be asked and answered freely.

This is something that we can do only if we are prepared to enter into serious conversation with all comers, including people with different views from ours. It is open debate with students, colleagues and society that makes the university more than a mere echo chamber for received wisdom.

I?recognise that the daily reality can be difficult. A truly open debate requires appropriate codes of behaviour and an atmosphere of safety. A university is much more a community than an organisation, and it can flourish only on the basis of good mutual relations. However, a community also runs the risk of excluding non-mainstream thinking. There is a danger that universities appoint mainly people who look and think like us. This is why the increasing focus on diversity is so important, not only in terms of gender, ethnicity and culture, but also ¨C maybe above all ¨C in terms of opinions.

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When you are searching for the right direction to take, it is always wise first to determine where you are coming from. Since Leiden¡¯s foundation in 1575, diversity of views has been the mainstay of our appointment policy. In the 16th and 17th centuries, scrupulous care was taken to ensure that different schools of thought were represented. If an Aristotelian was appointed, for instance, this was balanced by the appointment of a Cartesian.

There were important reasons for this. Gathering intellectual antagonists under the same roof acted as a kind of lightning conductor that not only contained the potentially incendiary electricity of controversy?but also redirected it to generate sparks of new knowledge.

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This is a tradition that universities should still cherish. It is why I am so happy with colleagues who throw themselves not only into scholarly debates, but also into public and political controversies.

That doesn¡¯t mean that there are no limits. Clearly, we are bound by the laws against inciting hatred. Equally, we are bound by academic integrity, which outlaws plagiarism or fabrication. And, of course, ensuring the physical safety of students and staff is a key obligation for every university.

But, for the rest, I say let the lightning strike.

This commitment to diversity of opinion also applies to those?whom we, including our students, invite to speak or write. The University of California, Berkeley made global headlines when it was accused of attempting to bar politically incorrect speakers. But as its dean of law, Erwin Chemerinsky, argues in a co-authored 2017 book, , the university has to be the forum ¡°for the new, the provocative, the disturbing, and the unorthodox¡±.

The book goes further. We should not let solidarity, community feeling, politeness or mutual respect ¨C important as these are ¨C take precedence over freedom of expression. Apart from the danger of appointing clones, there is also the risk that we are so pleasant and inclusive towards one another that we obstruct true debate. Diversity and inclusiveness ¨C two words that we so often utter in a single breath ¨C can at times lead to friction.

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The same is true within the classroom. In another 2017 book, also coincidentally titled , Sigal Ben-Porath, professor of education, political science and philosophy at the University of Pennsylvania, rightly argues that a sense of inclusiveness is especially important within this intimate environment. For instance, ¡°students on more liberal campuses who feel marginalized because of their [own] conservative¡­ideologies should sense that their views are respected and valued whether or not they are reflected in a particular syllabus.¡± And teachers should take care not to let controversies within class ¡°get out of control¡­damaging the relationships among students or between students and their instructor¡±.

But nor, Ben-Porath says, should controversy be avoided. Here, too, the lightning metaphor obtains.

I¡¯m sure that every university leader will have difficult cases ahead to deal with. But we have to guard against fearing ¡°the provocative, the disturbing, and the unorthodox¡±. Free speech at the university is not a given; it is something we have to work for every single day.

Carel Stolker is rector of Leiden University. This is an abbreviated version of his February address marking the anniversary of the university¡¯s foundation. The full version will be published open access in Places of Engagement: Reflections on Higher Education in 2040 ¨C A Global Approach (Amsterdam University Press) later this year.

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