Are design disciplines converging or diverging? Good question, but on what? I think the fundamental spirit of design has always been the same; designers work to better the human condition and to amplify ability. However, the diversity of the field is expanding as human experience expands. We can see similarities between practice and process — research, sketching, collaboration, prototypes and models, testing, refinements and the final build — are stages across architecture, visual design, interaction design and product design. (I would even argue these stages show up in engineering, though they look different.) The materials change, but the overall practice of design is consistent. As new technologies, materials and behaviors form, new design disciplines (or new discipline titles) are born.
I am often asked to explain interaction design, and sometimes I tell a story: web design has grown up. We started with paper interfaces for communication, and then along came the internet. Then we became web designers, as new languages were developed to construct the virtual world. As the interactivity on the web expanded, we became experience designers. We are now interaction designers, as we need to bring touchscreen and mobile experiences in the fold, as well as various other touchpoints in the interaction ecosystem. However, the process fundamentally remains the same, a process that starts with wide rough strokes that lead to ever refining circles through experimentation and iteration.
If the design disciplines are converging, they are converging on a holistic theoretical framework that brings together social, environmental, political, physical, economic and individual considerations. Larger systems thinking is underpinning much of the design practice today. so really this convergence on a holistic framework is a divergence of awareness to the systems and patterns of the universe. We are moving simultaneously outwards and inwards in our understanding of how design works and its impact in the world.