We all support the idea of public art, right? Well, when it works. There are undoubted successes – Maya Lin’s Vietnam Memorial, Kapoor’s “bean” in Chicago – but plenty of failures too. Public art is an “instrument” for the public good, but what exactly is that and how do we measure it? Aesthetics? Foot traffic? A “renewed sense of place”? If the ingredients for success are so elusive, why fund only from the public purse?