III. Concrete Relational Concepts (still more abstract, yet not
    entirely devoid of a measure of concreteness):  normally expressed by
    affixing non-radical elements to radical elements, but generally at
    a greater remove from these than is the case with elements of type
    II, or by inner modification of radical elements; differ
    fundamentally from type II in indicating or implying relations that
    transcend the particular word to which they are immediately
    attached, thus leading over to

 IV. Pure Relational Concepts (purely abstract):  normally expressed by
    affixing non-radical elements to radical elements (in which case
    these concepts are frequently intertwined with those of type III) or
    by their inner modification, by independent words, or by position;
    serve to relate the concrete elements of the proposition to each
    other, thus giving it definite syntactic form.

[Footnote 64:  Except, of course, the fundamental selection and contrast necessarily implied in defining one concept as against another.  “Man” and “white” possess an inherent relation to “woman” and “black,” but it is a relation of conceptual content only and is of no direct interest to grammar.]

[Footnote 65:  Thus, the _-er_ of farmer may he defined as indicating that particular substantive concept (object or thing) that serves as the habitual subject of the particular verb to which it is affixed.  This relation of “subject” (a farmer farms) is inherent in and specific to the word; it does not exist for the sentence as a whole.  In the same way the _-ling_ of duckling defines a specific relation of attribution that concerns only the radical element, not the sentence.]

The nature of these four classes of concepts as regards their
concreteness or their power to express syntactic relations may be thus
symbolized: 
               _
    Material _/ I. Basic Concepts
    Content \_ II.  Derivational Concepts
               _
    Relation _/ III.  Concrete Relational Concepts
              \_ IV.  Pure Relational Concepts

These schemes must not be worshipped as fetiches.  In the actual work of analysis difficult problems frequently arise and we may well be in doubt as to how to group a given set of concepts.  This is particularly apt to be the case in exotic languages, where we may be quite sure of the analysis of the words in a sentence and yet not succeed in acquiring that inner “feel” of its structure that enables us to tell infallibly what is “material content” and what is “relation.”  Concepts of class I are essential to all speech, also concepts of class IV.  Concepts II and III are both common, but not essential; particularly group III, which represents, in effect, a psychological and formal confusion of types II and IV or of types I and IV, is an avoidable class of concepts.