Robert: Speed limits on residential streets in Crownsbury are routinely ignored by drivers. People crossing those streets are endangered by speeding drivers, yet the city does not have enough police officers to patrol every street. So the city should install speed bumps and signs warning of their presence on residential streets to slow down traffic. Sheila: That is a bad idea. People who are driving too fast can easily lose control of their vehicles when they hit a speed bump. Sheila's response depends on the presupposition that ['with speed bumps and warning signs in place, there would still be drivers who would not slow down to a safe speed', "Robert's proposal is intended to address a problem that Robert does not in fact intend it to address", 'most of the people who are affected by the problem Robert describes would be harmed by the installation of speed bumps and warning signs', 'problems of the kind that Robert describes do not occur on any nonresidential streets in Crownsbury']