tendency to look away from the immediately suggested function, trusting to the imagination and to usage to fill in the transitions of thought and the details of application that distinguish one concrete concept (to farm) from another “derived” one (farmer).  It would be impossible for any language to express every concrete idea by an independent word or radical element.  The concreteness of experience is infinite, the resources of the richest language are strictly limited.  It must perforce throw countless concepts under the rubric of certain basic ones, using other concrete or semi-concrete ideas as functional mediators.  The ideas expressed by these mediating elements—­they may be independent words, affixes, or modifications of the radical element—­may be called “derivational” or “qualifying.”  Some concrete concepts, such as kill, are expressed radically; others, such as farmer and duckling, are expressed derivatively.  Corresponding to these two modes of expression we have two types of concepts and of linguistic elements, radical (farm, kill, duck) and derivational (_-er_, _-ling_).  When a word (or unified group of words) contains a derivational element (or word) the concrete significance of the radical element (farm-, duck-) tends to fade from consciousness and to yield to a new concreteness (farmer, duckling) that is synthetic in expression rather than in thought.  In our sentence the concepts of farm and duck are not really involved at all; they are merely latent, for formal reasons, in the linguistic expression.

Returning to this sentence, we feel that the analysis of farmer and duckling are practically irrelevant to an understanding of its content and entirely irrelevant to a feeling for the structure of the sentence as a whole.  From the standpoint of the sentence the derivational elements _-er_ and _-ling_ are merely details in the local economy of two of its terms (farmer, duckling) that it accepts as units of expression.  This indifference of the sentence as such to some part of the analysis of its words is shown by the fact that if we substitute such radical words as man and chick for farmer and duckling, we obtain a new material content, it is true, but not in the least a new structural mold.  We can go further and substitute another activity for that of “killing,” say “taking.”  The new sentence, the man takes the chick, is totally different from the first sentence in what it conveys, not in how it conveys it.  We feel instinctively, without the slightest attempt at conscious analysis, that the two sentences fit precisely the same pattern, that they are really the same fundamental sentence, differing only in their material trappings.  In other words, they express identical relational concepts in an identical manner.  The manner is here threefold—­the use of an inherently relational word (the) in analogous positions, the analogous sequence (subject; predicate, consisting of verb and object) of the concrete terms of the sentence, and the use of the suffixed element _-s_ in the verb.