This thesis analyses the constellations of actors and the tensions that shape the articulation between participation and design in participatory urban projects. It examines the conditions under which the same entity can organise participation and contribute to project design without weakening the democratic legitimacy of the process or its operational effectiveness.

Based on a literature review and interviews with urban planning and participation professionals, the thesis shows that the overlap of roles is not an anomaly, but the result of three dynamics: the recent institutionalisation of participation, the broadening of urban professions, and the still incomplete professionalisation of the participation field.

The analysis distinguishes two rationalities of justification: a normative approach, which emphasises positional effects and defends a strict separation of roles as a condition for the credibility of a listening space distinct from the logic of design; and a pragmatic approach, which starts from the project’s real constraints and considers that role overlap can be acceptable if the process includes the necessary safeguards.

These two rationalities do not, however, correspond to two closed camps. Rather, they reveal a divide over what should take priority: guaranteeing unbiased speech or making that speech operative within the project. In practice, positions are more hybrid: participation specialists are also attentive to the integration of contributions, while urban planners and hybrid practitioners may recognise the risks of bias linked to role overlap. The disagreement therefore mainly concerns the threshold at which safeguards are considered sufficient.