In Chapter 3 we saw a robust cross-linguistic tendency for non-displaced (underived) sentence subjects to be high on both the Animacy and Thematic Hierarchies, and for displaced (derived) subjects to be lower (than non-displaced subjects) on both scales. We saw this pattern both as a general property of grammar and as a specific property of the displacing predicate constructions, where evidence was available. In the present chapter we will look at experimental evidence showing that manipulating the animacy of the main clause subject can affect how adults interpret the structure of a sentence, as well as their assumptions about the meaning of the main clause verb. The main finding is that adults tend to interpret an animate subject agentively, and an inanimate subject as displaced: they take it to be either a patient of the matrix verb or an argument of an embedded predicate.

Studies of adult sentence processing are relevant for understanding child language acquisition for two primary reasons. The first is that adult linguistic knowledge is the target state that children are moving toward in their development. If children exhibit deviations from the pattern of behavior observed in adults (e.g. they make more errors in comprehension or production), these deviations can inform us about which aspects of grammar (or processing) are difficult for children. So differences between children and adults can be informative for understanding the path of development. But similarities between children and adults can be highly informative too, and this is the second reason it is useful to look at adult sentence processing.