What makes a bottle to be a bottle? The matter that forms it can't represent the actual bottle without the substantial form of a bottle. On the other hand, the substance itself of the bottle has an accidental form. So what exactly happens when the bottle falls down and breaks into small pieces? Is it an accidental change of the form of the substance (Aquino's 'dough' example) or is it a substantial change that leaves behind only the matter of the bottle?