In this volume, originally published in 1970, an attempt is made to examine the more logical aspects of thinking, such as the ability to abstract and the manner in which concepts develop. The author describes the features that had long been regarded as central to thinking by experimental and theoretical psychologists of the time and he places more emphasis on the part played by language in cognitive activity.

In the second part the author points out how such basic features of thinking as concept and hypothesis formation, inference making and the use of ordinary English are...