'What am I?' asks my son.
'A boy,' I reply, not listening.
'What's a boy?'
'A boy is someone with a ... A boy is human who is male.'
'What's a yewmanooizmale?'
My daughter is pondering separate cosmic mysteries on the sofa.
'Why does cat poo smell?'
These untiring interrogations exasperate me. They distract me from the serious business of the White Stuff catalogue or the Met Office weather bulletin. They also unnerve me, for their infant logic exposes the vastness of my own unknowingness. 'Why did Jesus have to die?' asks my daughter and I discover that, despite sharing a house with a theological library, I flounder. 'Why is water wet?' 'Why don't we have three arms?' 'Why doesn't my Lego tip over when Earth turns round?' I don't know and I don't know and I don't know.
Lately the questions have become more focused and just as foxing. 'What is eight times 13,' asks the nine-year-old, hunched over her maths homework. 'Who was Henry VIII's fourth wife?' 'Why do you never know the answer to anything I ask you?'
I wonder then why it takes children to reveal the holes in my intellect. In adult gatherings I can maintain a semblance of worldly wisdom as we debate how to remove ketchup stains from lambswool and whether Jason Donovan should have won Strictly Come Dancing. At which point the answer blinds me. The weight of years and insomnia have innured most of us to life's philosophical questions. My brain buzzes with shopping lists and school dates. I lack the mental space and energy to ponder why the wind is windy or what is the essence of Boy.
I am sobered by this. By the time the children are flown and I have the leisure of my own unimpeded thoughts, my mind will have shrunk too small to recapture cosmic curiosity.
I resolve to revise Tudors and times tables and to look up Existentialism on Wikipedia. And next time my son asks me why cats don't need hair cuts, I shall rejoice in his quest for enlightenment, even though my answer will be 'Don't know'.