Rare indeed, and bracing, are the moments that strip us of certainties and force us back to consideration of our most fundamental values. Such was 2016.

Mr Donald Trump campaigned to an America now largely dependent on televisual and social media-provisioned sources of information and misinformation. Institutions - such as newspapers, political parties and universities - that have traditionally helped test and vet evidence and argument hit, and now must face, the limits of their influence.

As a society, we find that our disagreements are deep and that many of us, perhaps even most of us, too easily personalise them. We are dangerously near treating one another as aliens.

Where to from here? The single most helpful resource I have hit upon is an old book by the Roman politician and intellectual Marcus Tullius Cicero. It's called On Duties. In it, Cicero offers guidance on navigating turbulent political times.

Remember, he says, your distinct roles and their specific responsibilities. It is fine to take on first one role, and then another, the persona of the father and then of the politician, for instance, or the persona of the philosopher and then the citizen. None of us needs to be just one thing.

But as we move from role to role, we must have clearly in view the responsibilities that pertain to each. One's duty is to perform the responsibilities of the roles one has entered into.

The mission of universities is to educate. The responsibility of professors derives from that mission. The grounding commitment is to truth.

The mission of a news group is to record accurately the course of events, including patterns of deception and duplicity. Again, the grounding commitment is to truth.

The mission of a citizen, an American citizen, is to defend America, indivisible, with liberty and justice for all. The grounding commitment is to human moral equality, as in the Declaration of Independence. This, too, entails a dedication to truth. "We hold these truths to be self-evident," reads the Declaration, as it introduces the fact of human moral equality.

America the Indivisible spreads opportunity wide and embraces all colours, all creeds within the sunshine of equal regard.

America the Indivisible looks at the divisions between rural and urban communities and seeks out bridge-building solutions.

America the Indivisible looks at patterns of racial and socio-economic residential segregation and inequalities in access to housing and transportation and seeks reinvestment in public infrastructure like transportation and housing that will connect communities now separated.

America the Indivisible defends its borders but welcomes strangers and recognises that those who have put down roots here and worked to build strong communities have earned our regard.

And America the Indivisible rejects invidious distinctions among potential immigrants - quota systems must go. Entrance should be by pure lottery from among those eligible on the grounds of security assessments.

America the Indivisible acknowledges the ravages of illegal drugs and seeks out solutions aimed at achieving the health and well-being of as many as possible touched by the world of drugs and at limiting the harm caused by drugs to the rest. It looks to places such as Portugal, where marijuana has been legalised and other drugs decriminalised, and adolescent drug use is down and the percentage of users seeking treatment is up. It does not look to the Philippines where a deepened investment in a "war on drugs" has metastasised into extrajudicial murder.

And America the Indivisible seeks to reduce the footprint of the criminal justice system so that we have funds to invest in public education, including state universities. Once upon a time, we led the world in spreading the benefit of education. America the Indivisible will rediscover the truth that education is a public good. It strengthens economies, communities and individuals by spurring human flourishing.

Each and every one of us can defend America the Indivisible - by running for office, at all levels; by seeking inclusiveness in every decision-making process of which we are a part; by supporting organisations and leaders who defend basic political and civil rights, equal protection of the law and due process, and basic human rights, especially for the most vulnerable among us.

We can defend America the Indivisible by reminding the anchor institutions of civil society to return to their core missions and to apply themselves assiduously to their responsibilities.

We can defend America the Indivisible by holding up the values we believe in, often and everywhere, with firm voices, clarity of commitment and charity towards those with whom we disagree.

We can defend America the Indivisible by telling the truth.

WASHINGTON POST

• The writer is a political theorist at Harvard University.