Chewing this over with my teenage daughter over breakfast one morning. I speak English, she answers in French:

Me: can ideas exist forever?
Her: yes, of course they can.
Me:  why?
Her:  because.
Me:  that’s not an answer.
Her:  if an idea has been thought, it exists.
Me:  so you mean every idea that has ever been thought, exists?
Her:  yes, because someone will still know they exist.
Me:  what about ideas that have never been written down, ideas that have been forgotten? Let’s say I have an idea but don’t tell anyone about it or write it down, and then I forget it, does it still exist?
Her:  it still exists.
Me:  but how can my idea exist if I’ve forgotten it?
Her:  you’re so self-centered (she says nombriliste in French, nombril being my belly button…). An idea doesn’t need you to exist!
An idea doesn’t need me to exist… all my ruminations on fiction and reality annihilated in an axiomatic instant. It takes me some time to recover. I stare at my daughter, who returns the gaze and notches it up one as if to say: wot you staring at?
Me:  so, ideas don’t… need… us… to exist… would you say God is an immortal idea?
Her:  yes. God is an immortal idea. And ideas don’t need you to continue to exist.
She keeps staring at me staring at her staring at me. How comes she finds (so) easy what I find (so) hard?