In the preceding chapter, we described and criticized the transformational and case models of underlying conceptual structure. Then we introduced the orrery model of underlying structure and compared it to the transformational and case models. Table 3.1 summarizes these comparisons. In this chapter we are going to present some experimental evidence suggesting that the features characterizing the orrery are supported by data on human language performance. That is, we shall support our claim that underlying structure is hierarchical, unordered, contains dependency information, and is lean.

First we discuss the distinction between structure and function as it pertains to experimental verification of models of language. Then we review some evidence to indicate that underlying structure is organized hierarchically rather than heterarchically. These findings favor the orrery and transformational models over the LNR version of case theory. Next we describe the work of Levelt, which supports hierarchical organizations, providing that the feature of dependency is present in the structure. These data favor the orrery model alone. Next we describe an experiment by Weisberg suggesting that left-to-right sequential information is not rigidly fixed in underlying structure. This finding favors the orrery and LNR version of case theory and makes difficulties for both the standard and case versions of transformational theory.

Next we examine the lean-rich dimension, comparing the orrery to the case model. All other things being equal, a simple model is better than a more complex model to explain the same thing.