"Practice is the only criterion for testing truth" has been widely recognized for decades, and recently it has been re-questioned by some people. It is said that an old gentleman also said that axioms can still deduce truth, so axioms are also a criterion for testing truth, and practice is not the only criterion.
My question is: Where do axioms come from? Did you come up with a head-on-the-head idea? Or is it derived from another "truth"? I guess not, right? Isn't it summed up from practice?!
Just as the phrase "all metals conduct electricity" has become an axiom, there is no need to test one by one whether each metal is electrically conductive. If a new metal is discovered, it is enough to deduce that it conducts electricity from that axiom. But can this be said to be the result of that axiom / not the fruit of practice?
Speaking of Newton, was it the law of "gravitational pull" that he saw when the apple fell to the ground first, or did he first come up with the law before he saw the apple fall to the ground? Isn't it still necessary to take the line of "coming from practice and then going back to practice"?
![In the French film "The Old Gun", the doctor with the scalpel raises the gun of revenge[fig]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)