Accessibility, usability and universal design - still confusing? Harmonisation of key concepts describing person-environment interaction to create conditions for participation.

Purpose: To contribute to an in-depth understanding of how the concepts accessibility, usability, and universal design interact and can be harmonised to create conditions for participation in the 21st century.

Material and methods: Ideas, empirical research, and selected literature from health science, engineering, and design constituted the material for a scientifically grounded analysis.

Results: We describe recent developments, how the concepts relate to and complement each other, and the synergies they create. Reflecting on the lack of clarity in their application, we argue that definitions are crucial and that the concepts can be combined and harmonised in a synergistic entity: The participation of all is the ultimate goal of society. Universal Design is the value-based vision and approach to design grounded in human rights that, through intersectionality and involvement, should permeate all aspects of society to create the best possible conditions for participation for all citizens. Accessibility and usability are tools for operationalising and translating universal design into practice, applicable at the individual, group, and societal levels.

Conclusion: Intended for implementation at all these levels, we propose a harmonised model where the concepts are explicitly defined and closely connected, with each other and the conditions to reach participation at scale.