A concept whose construction involves some element of transformation cannot be generated on the basis of existing mental representations. In this sense, it is mentally `impossible'.
Boden can then justify saying a concept is `new' on the grounds that it was previously `impossible'.
As she puts it `To justify calling an idea creative ... one must identify the generative principles with respect to which it is impossible.' (Boden, The Creative Mind, 1990, , p. 40)