I have a knife said George
It has a wooden handle
I have knife said Polly
It has a metal handle
I looked at them both and noted that I did not care what material the handle was made from
The blade was the most important part of the knife as without the blade would be a different thing and not a knife any more
The blade was its essential property and gives it its defining function
Plato and Aristotle believed this to be true
I have a knife said George
It has a wooden handle but no blade
It is therefore not a knife
I have knife said Polly
It has a metal handle but no blade
It is therefore not a knife
The item that we hold in our hands has no defining function and therefore does not exist
I handed both George and Polly two sharp blades but asked for the handles in return
Now that you possess the blades but not the handles do you each possess a knife
The siblings stayed silent and looked at me
The answer is no as you both once possessed handles and latterly you have been given blades
But neither broadly have a defining function
They only function together like our lungs and other organs
I gave George and Polly the handles but did not request the return of the blades
After a while they had both reconstructed their knives and handed them to me in exchange for a steam locomotive
I was too polite to refuse their offer