Karl Wilson Gehrkens, Essentials in Conducting
“ In concluding our discussion of dynamics, let us emphasize again the fact that all expression signs are relative, never absolute, and that piano, crescendo, sforzando, et cetera, are not intended to convey to the performer any definite degree of power. It is because of misunderstanding with regard to this point that dynamic effects are so frequently overdone by amateurs, both conductors and performers seeming to imagine that every time the word crescendo occurs the performers are to bow or blow or sing at the very top of their power ”
