Recently, Greenfield I has attempted to obtain evidence to support the idea that while children are limited to uttering single words at the beginning of language acquisition, they are capable of conceiving of something like full sentences. On the basis of the child's one-word utterance, the preceding context, and the child's actions, she has attempted to determine what it was the child intended to express. For example, one child said "fishy" on four different occasions. Greenfield interprets these four uses of the same word as each having a different conceptualization underlying it, such as those that would be expressed in the sentences: "That is a fish," "This is the fish book," "That is my fish," and "There is the fish's tank." Greenfield believes that the child is attempting to express and therefore can conceptualize nomination, possession, location, and so forth.
Although there is a great deal more evidence that the child intends to express these relations once he has advanced to two-word speech (especially the evidence from the consistent use of certain word ordering), children using one-word utterances do often seem to be expressing more than that single word; the concept of one-word speech as often being holophrastic seems to be valid.
There have been several recent studies of the acquisition of individual words, not as holophrases but as lexical units-that is, as units of meaning that can be used in building sentences. Various linguists, psychologists, and anthropologists have attempted to analyze "semantic fields" (groups of words that are in some way related). The basic idea behind these analyses is that the meanings of many words can be divided into combinations of smaller, more basic, units of meaning. These basic units of meaning are here called "semantic features." Other authors have called similar constructs "semantic components" or "markers" or "dimensions"; these labels will be considered to be synonyms for our purposes.
Semantic features are not part of one's vocabulary; they are not words, but abstract, theoretical elements, postulated in order to describe the relationships between words. In attempting to clarify what these semantic units are, Katz writes: