Given a set of objects in a category and a set of features by which they can be described. Then these can be arranged in a two-dimensional table each of whose cells contains the value that each object has for each feature.
For any feature of the set, the object entries of the table can be arranged in such a way that the cells that contain the same value are contiguous. If the objects can be arranged in such a way for all of the features simultaneously, then there is an intrinsic connection among the features. If the break-off point of the feature values does not coincide between two particular objects, but ranges over the entire set, then there is no non-arbitrary way to divide the set into two distinct categories. Instead, for each of the features an implicational generalization may be formulated of the form ‘If an object has an α value for any of the features, then all the objects to its left in the table also will have the α value for that feature.’ A table of this logical form is called a gradience (in the 1970s a “squish”).
Corbett 1978:358 presents a table of the grammatical properties of Russian numerals which is a particularly clear example of a squish. See the references there to Ross 1972ff.