The Structure and Development of Logical Representations in Thought and Language

The expressive power of human thought and language comes from the ability to systematically combine a finite vocabulary of concepts into a boundless number of meaningful thoughts. What properties of conceptual representations enable their combination? Three papers investigate different aspects of the combinatorial system in the context of a single general approach – taking logical concepts as a special case of concepts whose content is completely specified by their combinatorial properties. The first paper looks at infants’ ability to represent two types of goals: approach and avoid, where each goal-type could be represented as the negation of the other. Consistent with past literature, we find evidence of children representing approach at 7 month, but failing to represent avoid at both 7 and 14 months. This suggests that these children cannot combine their representation of approach with a negation operator, possibly because they do not yet have this operator. In the second paper, we continue to look at the emergence of logical negation through the relationship between the emergence of the concept and the words that label it. We find that, although 15-month-olds say the word “no”, they do not understand its logical meaning until 24 months. This is the same age at which they begin to produce the word “not”, comprehend its logical meaning, and use both “no” and “not” to deny the truth of others’ statements. This pattern of results suggest a common limiting factor on the mapping of any word to the concept of logical negation. This factor could be the emergence of the concept, or a linguistic limitation common to both “no” and “not”. The third paper looks at the properties of the combinatorial system in adults, taking linguistic quantifier scope ambiguity phenomena as a case study. Using a priming paradigm, we find evidence for independent combinatorial operations for the universal quantifiers EACH, EVERY and ALL, but common operations for the numbers THREE, FOUR and FIVE. We also find that the semantic operations that compose quantifier meanings abstract away from the verb and noun content of sentences. This suggests a division of labor in adult combinatorial thought, with conceptual content represented separately from the combinatorial properties of concepts.
Psychology