's workings? In 1868, the Dutchman Frans Donders suggested that a start be made with a "subtraction method." For instance, he said, the time required to add two one-digit numbers could be found by subtracting the time it took to add four such numbers from the time needed to add five. Donders studied many mental operations in this way.
Modem cognitive psychology might have developed from that simple beginning, but it did not. Donders's work was attacked.
Critics argued that his method...