Structural Environments There are certain symbols which (1) stand for other symbols or (2) mark relationships between symbols. Pronouns illustrate the first type. [...] The meaning of any pronoun must be defined in terms of the linguistic symbols for which it may substitute. Such an environment is stricly limited, though sometimes it is possible to provide nonlinguistic parallels from the practical world (as with English 'she') [...] Some morphemes symbolize the relationships between linguistic symbols. For example, in the German sentence 'Der Knabe sah den Mann' 'the boy saw the man' the suffix '-r' of 'der' signals that 'der Knabe' 'the boy' is the subject of the sentence, and the suffix '-n' of 'den' signals that 'den Man' is the object of the verb. The meaning of '-r' and '-n' are definable in terms of the linguistic environment of German syntactic constructions.
- Nida (1949), a pag.153-154