Having watched our mother lose her memory over a dozen years to the point where she doesn’t know who we are, my brothers and I wonder what goes on in her head. What’s it like to have dementia? We can never know until we are demented, and how useful will an answer be then? The best insight I have had into understanding what it is like to be demented is from watching The Father, a film directed and co-written by Florian Zeller and starring Anthony Hopkins, who won an Oscar for his performance.

We see father from both inside and outside. At the beginning his daughter has come to see him because yet again he has got rid of his carer. She tries to explain to him that he needs somebody to care for him or else . . . We all know what the “or else” is, he will have to go into a home. Father refuses to accept that he needs anybody to care for him. The beginning is thus familiar. The daughter also tells him that she has fallen in love and is going to live in Paris—and won’t be able to see him often.

In the next scene father walks into his living room to see a strange man sitting there. “What are you doing here? Get out of my flat.” The man answers that he lives here, and we, the audience, become confused. We know that father lives on his own. Then we learn that the man is the daughter’s husband, but we thought that she was going to live in Paris with a man that she’d just met. How can she have a husband? Father tells the man that he has bad news for him, that his wife is going to live in Paris with another man. The stranger doesn’t think so. Then the daughter arrives, played by another actress but of a similar build and with a similar short haircut. I couldn’t understand who this woman was, but my wife immediately recognised that this was the daughter. I was confused.

I reflect how my mother knew who I was until a few years ago but then became ever less sure. She has introduced me to others as her father.

In another scene the daughter’s husband is played by another actor, and this husband tells father that he is “getting on our tits” and gives him a shove.

The daughter tries another carer, a young woman very used to people with dementia. Father performs for her, telling her he was a dancer and demonstrating his ability to dance. I’ve seen this confabulation in our mother many times. She’s also disinhibited.

The final scene is in a nursing home, a palatial one, and the nurse who cares for father is nothing short of loving. Few of us will have such care.

The film gives us insight into what it might be like to have dementia as we the audience become steadily more confused over who is who and whether stories are true or imagined. Wonderful to watch and beautifully acted, the film provides some answer to the impossible question of what it is like to be demented.

Richard Smith was the editor of The BMJ until 2004.

Competing interests: none declared.