So, what is needed to begin the change that must come to our city? In the classes I teach to undergraduates at Johns Hopkins, we talk about the social determinants of health — i.e. what are the factors in a person's environment that impact their health and their community's health? The conclusion we have reached is that for a neighborhood, a community, or a city to be truly healthy, a "four-legged stool" must be in place. As with an actual stool, providing just one, two or even three of the legs will not keep the stool from falling down — all four legs must be present and sturdy.