Abstract
According to the thesis of semantic underdetermination, most sentences of a natural language lack a definite semantic interpretation. This thesis supports an argument against the use of natural language as an instrument of thought, based on the premise that cognition requires a semantically precise and compositional instrument. In this paper we examine several ways to construe this argument, as well as possible ways out for the cognitive view of natural language in the introspectivist version defended by Carruthers. Finally, we sketch a view of the role of language in thought as a specialized tool, showing how it avoids the consequences of semantic underdetermination.