We’re not born with theory of mind, the cognitive capacity to attribute to others emotions, beliefs and motivations that don’t match our own. Theory of mind enables you to chuckle fondly at your forgetful friend, even though you have three reminders set for every important birthday or anniversary. Theory of mind is what allows you to respect the different beliefs of someone of another cultural, political or religious identity. It’s what makes you understand how a person could make a choice you think you wouldn’t make in a difficult situation, without simply deciding they’re ignorant or wrong. Theory of mind is what permits us to grant others the same complexity, compassion and nuance that we apply to ourselves. It is a signal of emotional maturity.My niece Astrid apparently developed theory of mind just this month, or at least made strides, which is more or less on schedule. She’s six. That’s just about the age at which we have a profound realisation – it occurs to us that people around us can feel an emotion without necessarily showing it. Astrid turned to my brother, her dad, and for the first time asked him where his own daddy is. She realised that he, like herself and her little brother, must presumably have a father. My brother explained, in age-appropriate terms, that his dad, like his mum, was dead. I’m not sure how deeply my niece understands what it is for a person to be dead, but she grasps that it’s serious and it means some kind of very big absence; bigger than any she’s encountered. She’s also grasping what it means for there to be things that exist but that she hasn’t encountered, which is to understand that there are minds and a reality outside one’s own experience – childhood is an emergence from solipsism. We’re all philosophers when we’re small and we wrestle with the biggest and most baffling questions for the first time. “You must be sad that your mum and dad are dead,” Astrid said seriously to my brother. “You must,” she was implying, “be feeling something that I cannot see”. This is a pretty complicated piece of cognition for a person who gets to school on a unicorn kick-scooter every morning.Our father died last December and Astrid never knew him. His death was as sad as his life had been – a testament to lost potential and decades of harm. He did not have much in the way of theory of mind. In my father’s internal world, everything was filtered through and in service to his own emotions. He built stories about other people which made him feel justified in relegating them to supporting cast members in his own story. Astrid was protected from him in a way my brother and I had not been. And so, while she never knew him, his absence hasn’t been a constant narrative in her short life. When I was her age, I had already begun often to wonder where my father was and why he always seemed so angry when he was around. I had already learned to be afraid of him. She sadly will never have a loving grandfather, but neither will she have one she learns to be afraid of; and so, something changes. Something broken was not passed to the next generation; not given the opportunity to gorge itself darkly and grow. That is what parents do for their children, if they are capable of doing it. If they have theory of mind and can pity the internal deficit that would lead a man to harm and neglect his children, while recognising that they themselves can do better, and will.I saw my niece for the first time since moving back to London a few weeks ago. She had come with her mum and dad to see the Arsenal team celebrate their first Premier League title in 22 years. My brother has loved the team from as long as I can remember – since he was about Astrid’s age, with little legs and a round, pink face. I considered what he would have given, as a small boy, to see a parade like that, hand in hand with his own father.I considered it as I watched my brother and Astrid walk together, hand-in-hand, to celebrate with the other fans. Both were in their jerseys, though only Astrid had the matching shorts. In honour of the occasion, my niece had been given and permitted to use the most annoying klaxon in the known universe. She would intermittently blow through it to create a noise more obnoxious than the human imagination could conjure. Each time the din blasted out, an expression of sheer bliss twinkled over her luminous little face. It was the best a thing can be when you’re six – loud, attention-grabbing and forbidden under any normal circumstances. The afternoon rings out with her happiness.“Where is J?” she asks me later, when we’re sitting together underneath the kitchen table and whispering secrets. J is my husband, who she likes because when they’re together he tips her upside down on the pretence that he’s sure she’s got sweets hidden in her pockets, and because he helps her make towers out of Lego despite her exacting project-management standards. “He’s still in Australia,” I say. I’d moved back to London by myself for work. “And Mabel?” she asks. “Mabel too,” I tell her. Mabel is the cat. “Oohhhh,” Astrid says, her face scrunching a little as she thinks about this new kind of big absence. A long pause ensues. “Do you miss them?”“I do,” I say. “But missing is a nice feeling, because you miss someone when you love them. Isn’t that nice? To love somebody so much and to know they love you back?” She looks at me ponderously, her mind doing its secret work, and we sit quietly together under the table until her dad comes to find us.