John E. Arnold was one of the first authors to use the term 'design thinking'. In "Creative Engineering" (1959) he distinguishes four areas of design thinking. According to Arnold, design thinking can yield (1) novel functionality, i.e. solutions that satisfy a novel need or solutions that satisfy an old need in an entirely new way, (2) higher performance levels of a solution, (3) lower production costs or (4) increased salability. Thus, according to this early concept, 'design thinking' covers all forms of product innovation, including especially incremental innovation ("higher performance") and radical innovation ("novel functionality"). Arnold recommends a balanced approach: Product developers should seek opportunities in all four areas of design thinking.