ABSTRACT
Before analysing the conservation and measurement of length we need to study how children judge distances and how they achieve their conservation. It may be that common usage makes no sharp distinction between the concept of distance and that of length. But psychologically they point to two quite different situations which become interdependent only as a result of a gradual development. We must therefore study them separately. On the one hand, there is the question of the linear size of objects like sticks or the paths along which we walk. We shall use the term ‘length’ to denote this kind of size. The term ‘length’ will therefore refer to the size of filled space, i.e. to objects as such. ‘Distance’ will be used to refer to the linear separation of objects, i.e. to empty space.
