What syntactic or morphological characteristic defines SLI?

The characteristic that defines Specific Language Impairment (SLI) is indeed shorter Mean Length of Utterance (MLU) and the omission of obligatory morphemes. Children with SLI often demonstrate challenges in their language development compared to their peers, particularly in the areas of grammar and morphology.

A shorter MLU indicates that the child produces sentences that are less complex and shorter than expected for their age group. This is a common feature seen in individuals with SLI. Additionally, the omission of obligatory morphemes, such as tense markers or plural endings, is another hallmark of SLI. These children may frequently leave out essential grammatical elements that are typically present in the speech of their peers, leading to simpler and less grammatically accurate utterances.

In the context of language development, the absence or incorrect usage of these morphemes signifies a gap in the understanding of language rules, which is characteristic of SLI. Therefore, the option highlighting the shorter MLU and omission of obligatory morphemes accurately encapsulates the syntactic and morphological issues associated with SLI.