Sensiblesubstanceischangeable。Nowifchangeproceedsfrom
oppositesorfromintermediates，andnotfromalloppositesforthe
voiceisnot-white，butitdoesnotthereforechangetowhite，
butfromthecontrary，theremustbesomethingunderlyingwhich
changesintothecontrarystate；forthecontrariesdonotchange。