This essay, on politics and demography, was my Observer column this week. It was published in the Observer, 27 January 2019, under the headline ‘Demography is not destiny. Politics should be about winning minds’.

Peter Kellner’s ‘crossover day’ has caused some commotion. Last Saturday, according to the veteran pollster, Britain became a majority Remain nation through demographic changes alone. Kellner’s calculations suggested that in the period since the 2016 referendum, sufficient old folk (who largely voted Leave) had died and enough teenagers, overwhelmingly Remain, had reached voting age to have wiped out the majority for Brexit.

Remainers seized on Kellner’s projections as ammunition for a second referendum. Critics (not all Leave supporters) condemned them as being, in the words of the Labour MP Caroline Flint, ‘unhelpful, ageist and divisive’. Whichever view one takes, the ruckus over ‘crossover day’ reveals the way that political demography – the study of the relationship between population changes and political attitudes – has become increasingly central to public debate.

Understanding demographic changes is undoubtedly important. An ageing population, changes in family sizes, shifts in the gender balance in the workplace – all have implications for policymaking and the allocation of resources.

Demographic analyses of political attitudes can also provide valuable insights. The demographic breakdown of the Brexit vote or the changing role of class in voting patterns can help illuminate significant social trends. Demography has, however, come to be more than an aid to policymaking or political strategy. It has increasingly come to be seen as a causal attribute. There is, many suggest, a fundamental link between demographic traits and political attitudes. It’s a perspective that leads people to assume that which needs to be explained. We know, for instance, that those who voted Leave were likely to have been less educated than those who voted Remain. Many took this as evidence that Brexiters voted as they did because they were uneducated, hence ignorant. But as the political scientist David Runciman has observed, a better explanation may be that education is no longer simply a means to knowledge but has, rather, become a marker of one’s values and worldview. Simple demographic arguments can blind us to the complexities of social change while also entrenching prejudices.

The obsession with demography has led to the fetishisation of certain groups and to the demonisation of others. The young are seen by many as the vanguard of liberalism and an open society. But while most young people are highly tolerant of diversity, many are also ambivalent about the merits of free speech and of democracy.

The old are castigated for their illiberalism and narrow-mindedness. But the 65-plus cohort is also the generation that helped foment the 60s revolution that transformed attitudes to sexuality, diversity and equality.

There is more here than a simple demographic cleavage between liberal youth and the illiberal elderly. What we are witnessing, rather, is likely to be a complex interplay of age, class and ethnicity against the background of a political system in turmoil.

An obsession with demography can also lead to a lazy, even cynical, form of politics in which politicians, rather than trying to win arguments, assume that minds cannot be changed and seek instead to appeal to particular groups and to tailor their message to what they assume those groups want to hear. This attitude is perhaps best expressed in Donald Trump, who cares little about changing minds but sets out primarily to consolidate his base.

On the left, too, this approach is becoming more ingrained. It’s the left, though, that will most suffer in the reduction of politics to demography.

We can see this in America in the raging debate within Democratic circles over whom the party should target in the 2020 presidential elections – white workers or minority groups. We can see it, too, in Labour’s Brexit prevarications; instead of setting out a clear policy and aiming to win people to that stance, the Labour leadership seems to think it better to send different messages to different groups on either side of the Brexit divide and to make a virtue of evasion.

In an age in which the politics of identity has become entrenched, demographic arguments inevitably have purchase. Ideals and values become seen not just as a terrain of political contestation but also as measures of tribal attachment.

The significance of the ‘crossover day’ argument was the claim that Britain had become Remain not because opinions had changed but because the electorate had. From one perspective, this was simply a statistical insight about a political swing arising out of demographic shifts. From another perspective, it entrenches the view that the motor of change is demography rather than politics. That’s a road we should all be wary of taking.

The image is one of Japanese artist Aoki Tetsuo’s ‘People’ illustrations.