Parallel thinking, the basis of the Six Thinking Hats method, requires looking at a situation or question from different viewpoints and accepting all of them, no matter how contradictory they may seem. After the matter at hand has been thoroughly reviewed through a series of thinking “hats,” or modes, then the decision-makers can either choose the best one or create a design that covers the best possibilities. Thus, throughout the book, de Bono emphasizes the importance of parallel thinking.

De Bono contrasts parallel thinking with what he regards as traditional Western or argumentative-style thought, which has come down through the centuries from the ancient Greek philosophers Socrates, Plato, and Aristotle. The author finds several dangers in an argumentative approach to an issue. It can be confusing, because the thinkers don’t sort out factors such as emotions, information, logic, hope, and creativity that affect their thought. It can also be ineffective for people who are only able to think in one dominant mode, particularly when it is far easier to be negative about an issue than to be positive. Furthermore, it can lead to demonstrations and clashes of ego, which many cultures consider to be aggressive and nonconstructive.