4. A performative definition of sentence relatedness.
Three sentence families were constructed and the semantic relations among the<br />members of each family were investigated experimentally. A scaling technique was developed to allow subjects to evaluate the degree of semantic similarity between each pair of sentences in each family. It was found that pairs of sentences normally related by optional transformations were judged most similar by subjects. However, a strong semantic cohesion appeared among all yes-no questions but such a cohesion did not appear among the declaratives. Such results are not predicted by a formal grammatical analysis. It was concluded that the intuitive notion of semantic similarity so often adverted to in formal descriptions is very different from the naive native speaker's notion of semantic similarity.