The study of syntax in typically developing children has led to the development of theories accounting for apparently ungrammatical structures. One such theory is truncation theory (Rizzi, 1993/1994), which states that because of computational limitations and a tendency to choose the most “economical” structures, children’s early grammar tends to prune the syntactic tree of its more complex layers. The more mature the child’s grammar, the less layers they will truncate, and the more complex their syntax will be. For a general introduction to syntax and a detailed explanation of truncation theory, please refer to Appendix I.
Several theories have been proposed to tap into the mechanisms underlying principles of economy such as postulated by Rizzi (2000). These theories establish predictions pertaining to the types of syntactic structures that would be simpler or more complex for children to process. Relativized Minimality (Rizzi, 1990, 2004) and Derivational Complexity (Jakubowicz, 2005, 2011) are two of the most influential such theories, and form the basis for our hypothetical metric of syntactic complexity. They are of crucial relevance for this study, and are explained in detail in Appendix I.
Predictions arising from Relativized Minimality (RM) and the 1.1
Derivational Complexity Metric (DCM)
In the Derivational Complexity Metric (Jakubowicz, 2005, 2011), the most important factor that influences complexity would appear to be movement. A structure containing the movement of an element will be more complex to process than a structure containing no movement.
In Relativized Minimality (Rizzi, 1990, 2004), two factors seem to influence the complexity of any given syntactic structure: intervention and similarity. A structure containing an intervener that is similar to the target will be more difficult to process than a structure containing an intervener that is different, and even more so than a structure containing no intervener at all.
Combined, these two theories could therefore lead us to postulate the existence of three factors determining syntactic complexity, and thereof children’s performance: movement,
intervention and similarity. Similarity arises only when the sentence contains an intervener, which can only appear when there is movement in the sentence. It is therefore possible to surmise the following metric of complexity, from most syntactically simple to most syntactically complex:
1. No movement 2. Movement only
3. Movement and intervention with a dissimilar intervener 4. Movement and intervention with a similar intervener 1.2 Sentential complements
Sentential complements are comprised in the highest level of the syntactic tree, as are wh-questions and relative clauses. A sentential complement is a subordinate clause embedded in a main clause, functioning as an argument of a verb in the main clause, such as in (5).
(5) She hoped [that it would soon end.]
In this example, “She hoped” is the main clause, and “that it would soon end” is the subordinate clause or sentential complement. A particular feature of sentential complements is the type of verb that is used in the main clause, or matrix verb. Matrix verbs comprise several types of verbs such as verbs of communication (e.g. “say”), verbs of perception (e.g.
“see”) and mental state verbs (e.g. “hope”). These types of verbs can take complement clauses.
There are several kinds of complement clauses, that depend on the presence of complementizers such as “that” and whether or not the verb is finite. For example, the following sentence is a nonfinite complement clause, since its verb is nonfinite and it is missing a complementizer:
(6) Jane saw [the dog attacking].
Sentence (7) is a finite complement clause, since its verb is finite and it contains a complementizer.
(7) Jane thinks [that the dog ate the bone].
In this paper, we will be studying finite complement clauses, because of their purported role in theory of mind development (see below).
The matrix verb of a complement clause can belong to one of several different classes.
Noonan (1985) categorised matrix verbs into different types according to their semantics (e.g.
utterance, pretence, knowledge), and Kiparsky and Kiparsky (1970, cited by Poltrock, 2011) categorised matrix verbs into factive, nonfactive, or counterfactive according to the truth-value of the complement clause.
This is of particular interest to us, as the different types of verbs imply different truth values in the complement clause, which in turn interacts with the children’s cognitive abilities in order to understand the sentence. For example, factive verbs (such as verbs of knowledge, e.g. know, discover; and commentative verbs, e.g. regret, be sorry) are followed by a true embedded clause such as in “He regrets that the train left”, where the train must have left for the sentence to be pragmatically felicitous. Nonfactive verbs - such as propositional attitude verbs like think or believe- or communication verbs like say can be followed by an embedded clause whose truth value is undetermined, such as in (6), where the dog may or may not have eaten the bone, and in either case the sentence is pragmatically felicitous. To understand a complement clause containing a nonfactive verb, the child (or adult) has to have understood that the truth value of the complement clause is undetermined, and not take it at face-value. A third category of matrix verbs is the counterfactive category. Counterfactive verbs, comprising pretence (e.g. pretend) and desiderative verbs (e.g. want, wish, desire), require the embedded clause to be false, such as in “He pretended that he was a fox”.
These different types of verbs appear at different stages of children’s development. It would seem that communication verbs are acquired before mental state verbs, perhaps because “the propositions embedded under verbs of communication can be evaluated with respect to their truth as acts of speaking are overt whereas acts of thinking are not.” (Poltrock, 2011).
Furthermore, certain types of mental state verbs have been found to be used more often by young children. What Bloom et al. (1989) label as “epistemic” verbs (e.g. think, know), are used more often in finite complement clauses than sensory verbs (e.g. see , look) (Bloom et al., 1989).
In a comprehension task where children had to answer yes/no/maybe to the truth of an embedded proposition under nonfactive, factive or counterfactive matrix verbs, Schulz (2000)
(cited by Poltrock, 2011) found that the 4 to 6-year-old children correctly interpreted the different truth values depending on the type of verb presented.
The existing research pertaining to typical development of complement clauses in children’s speech would seem to point to 3 and 4-year-old’s inability to embed the complement under the matrix verb. Children of this age limit their sentence production to real states of affairs, and do not seem to understand the potential to express false propositions (Poltrock, 2011).