chapter  9
40 Pages


IN THE preceding chapters the errors discussed have been sorted into three main categories. There are, first, the structural errors: errors which arise from some failure to appreciate the relationships involved in the problem or to grasp some principle essential to solution. An error of this kind occurs, for instance, when a child interpolates in a series extrapolation problem; or when he thinks that successive pieces of negative information about the same term in a matching problem are pieces of information about different terms (the belief that there are 'two Dicks' in Problem A2).