The “backward effect” of an idea is the process of looking backward at past experience to assess the idea. The process uses judgment to make comparisons. For much thinking, such judgment is important, but with green hat thinking, judgment is replaced with movement.

Believed facts arise from comments made in good faith or personal beliefs. They can be put forward under white hat thinking, but de Bono stresses that they are “second-class” facts. Only believed facts found to be useful should be considered, and they must be verified.

Checked facts can be verified. They are not used to further a point of view, as believed facts sometimes are used. Instead, they are approached with neutral objectivity.