Again from Dick Buchanan, in his Governing Ideas white paper for Carnegie Mellon’s School of Design:

1. Designers must be inventive in conceiving the possibilities of a product.

2. Designers must be able to judge which of their inventions are viable in the contingent circumstances of manufacture and human use.

3. Designers must be able to make connections among many fields of knowledge essential for the development of a product and, based on such connections, draw reasonable conclusions or make decisions about the plan of a product.

4. Designers must be able to evaluate the results of conception and planning and choose a final solution based on values, preferences, and goals before a product is carried forward to clients and, ultimately, to human users.

So it’s all about Creating, Judging, Deciding, Choosing:

“The real subjects of the new intellectual free trade among the many cultures are our own thought processes, our processes of judging, deciding, choosing, and creating.” — Herb Simon, The Sciences of the Artificial

Update: Jamin Hegeman, MDes 2008, recently posted on Buchanan’s latest thoughts re: the core competencies of design: http://jamin.org/archives/2008/core-competencies-of-design/