The answer is motif :) any reoccurring theme, pattern, idea, image etc. in a work applies to this.
for example, an artist that includes flowers in across all of their work (or a series of it) would be depicting a floral motif. I hope this helps!!
These rules should apply to everyone tbh especially the first one...
So he can begin to learn without him.
Answer: decrescendo
Explanation: it means to gradually decrease in volume
It was invented by Alhazen so I don't know if the same applies.