This article offers a new strategy for cognizing musical indeterminacy based on Richard Sennett’s “five open forms for the city,” an intrinsically spatial way of thinking about what is “open” and how it is open. Sennett’s five forms (“synchronicity,” “punctuatedness,” “porosity,” “incompleteness,” and “multiplicity”) are explored individually as they impact our understanding of openness and/in music, illuminated by examples from contemporary experimental music.