Morphemes and combinations of morphemes are definable in terms of the various phenomena for which they are symbols. Fox example, they may be symbols for (1) objects: 'horse', 'cow', 'sun', 'moon', 'tree', 'grass'; (2) relationships: 'in', 'from', 'behind', 'high', 'low', 'one', 'two'; (3) abstractions: 'good', 'bad', 'red', 'true'; (4) processes: 'run', 'walk', 'speak', 'swim'; and (5) states: 'sick', 'full', 'be'.
- Nida (1949), a pag.152

[T]here are three functional types of symbolization: (1) signals for objects (this is in broadest sense of the term), (2) signal for classes of signals (these are pronouns and other types of substitutes), and (3) signals for relationships between signals. To define the meaning of any of this types of symbols we must refer to the environment in which they are employed. In the first istance, we refer to the practical world and to subjective reactions of speakers to the signal for practical-world objects. In the second two instances, we refer to the linguistic environment. There are some slight connotative differences perceptible in these second two types, but they are very minor in comparison whith those conveyed by the first type.
- Nida (1949), a pag.154