It may be possible to contrast one contour with another, in a single environment, and to find that contours 'A' and 'B' are equivalent except at one point while contours 'A' and 'C' are equivalent except at another point. In such cases we would say that the section of difference between 'A' and 'B' is one element, the section of difference between 'A' and 'C' another. These would be successive phonemic elements of contours, and the contours could be identified as consisting of them.
- Harris (1951), a pag.57