ABSTRACT

Measurement has always been central to experimental science, and the data with which scientists are happiest are numbers produced by measuring instruments like rulers, voltmeters, thermometers and chronometers. For Psychology, quantifying the phenomena it studies has been a perennial problem. For many thinkers, such as Immanuel Kant, it was the apparent impossibility of doing so which excluded Psychology from natural science. Furthermore, while, as the American psychologist E.L. Thorndike said, ‘everything which exists must exist in some quantity and can therefore be measured’, the converse is not necessarily true: everything which can be measured does not necessarily exist. This paradox will become clearer later. There is, moreover, the question of the relationship between the measurement as such and what is being measured. How do you measure something without changing it? This riddle arose first in physics (where the answer is an unambiguous ‘you can’t’), but we are coming to realise that it arises in Psychology too. It must be stressed then that the nature of measurement raises deep philosophical questions and present-day historians and philosophers of science have revealed it to be a less straightforward and logical matter than one might initially assume. Only some of the more immediately accessible of these questions can be touched on here.