We tested four predictions based on the assumption that optional infinitives can be attributed to properties of the input whereby children inappropriately extract non-finite subject-verb sequences (e.g. "the girl run") from larger input utterances (e.g. "Does the girl run?" "Let's watch the girl run"). Thirty children…

Purpose: Our purpose was to test the competing sources of input (CSI) hypothesis by evaluating an intervention based on its principles. This hypothesis proposes that children's use of main verbs without tense is the result of their treating certain sentence types in the input (e.g., "Was 'she laughing'?") as models for declaratives…