This article explores the nature of conceptual models for designing service participation. Conceptual models are both a representation and a hypothesis, dialectically creating conditions of participation. I first study the nature of a conceptual model and then explore the four arts with focus on the notion of form. Each art reveals a mode of thought regarding the form of the participatory whole: grammatical model of coproduction, rhetorical model of argumentation, poetic model of experience, and dialectic model of commitment. Along with the arts, I present case studies of four distinctive conceptual models that have been used to design for participation.