In an increasingly polarised world, dividing individuals into “us v them” and “allies and enemies” has become a pervasive mindset.

We arrange ourselves as “for” or “against”, whether it be political parties, vaccinations, climate change or the voice to parliament. We align ourselves with different sides of various wars. The negative effect of this on society is frequently noted. However, the more subtle and harmful effects on our mental health are often overlooked.

There are some obvious advantages to in-group formation. From an evolutionary standpoint, it allows for both the protection and sharing of the group’s resources. It fosters a sense of belonging and connection that promotes social cohesion and mental wellbeing.

It is natural for the human mind to categorise and take mental shortcuts. Research highlights the cognitive benefits of this simplification, but it also warns of the costs – specifically the loss of complexity and nuance. The loss of our ability to think beyond yes or no, in or out, is the loss of a vital human capacity.

The effects of this loss are particularly stark when the out-group is seen not only as different, or perhaps misguided, but also as indiscriminately threatening and hostile. At this point the cost to both the individual and society escalates and political, moral, ethical and material issues become urgent to address. However, there are also crucial psychological problems at stake. Whatever the causes of the original divide into enemies and allies,........

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