This paper argues that the widespread beliefthat ambiguity is beneficial in designcommunication stems from conceptual confusion.Communicating imprecise, uncertain andprovisional ideas is a vital part of designteamwork, but what is uncertain and provisionalneeds to be expressed as clearly as possible.Understanding what uncertainty informationdesigners can and should communicate, and how,is an urgent task for research. Viewing designcommunication as conveying permitted spaces forfurther designing is a useful rationalisationfor understanding what designers need fromtheir notations and computer tools, to achieveclear communication of uncertain ideas. Thepaper presents a typology of ways that designscan be uncertain. It discusses how sketches andother representations of designs can be bothintrinsically ambiguous, and ambiguous ormisleading by failing to convey informationabout uncertainty and provisionality, withreference to knitwear design, wherecommunication using inadequate representationscauses severe problems. It concludes thatsystematic use of meta-notations for conveyingprovisionality and uncertainty can reduce theseproblems.