The basic operations are those of segmentation and classification. Segmentation is carried out at limits determined by the independence of the resulting segments in terms of some particular criterion. If 'X' has a limited distribution in respect to 'Y', or if the occurrence of 'X' depends upon (correlates completely with) the occurrence of a particular environment 'Z', we may therefore not have to recognize 'X' as an independent segment at the level under discussion.
- Harris (1951), a pag.367