TRIZ and C-K are both presented as theories aiming to facilitate innovations. In recent years several authors have published articles enlightening differences between TRIZ and C-K. C-K was initially a descriptive theory of innovation, which has gradually been developed into methods with an operational focus. To clarify if both TRIZ and C-K could be recognized as theories, a first question will be considered, what is a theory? Are then TRIZ and C-K design theories, and if so, is it possible to consider two different theories of a single subject? This article is a first step in a more global perspective aiming at clarifying what a design theory should be and how these two proposals give part of answers, and they could be complementary.