The following is an excerpt from John Culvenor and Dennis Else – Engineering Creative Design
White Hat on the Hats
There are six metaphorical hats and the thinker can put on or take off one of these hats to indicate the type of thinking being used. This putting on and taking off is essential. The hats must never be used to categorize individuals, even though their behavior may seem to invite this. When done in group, everybody wear the same hat at the same time.