This new PNAS paper is so interesting! The authors asked a fascinating question: Do we need language to reason logically? They combined brain imaging in healthy adults with tests of two rare patients who had extensive damage to the brain's language network and profound aphasia. Both patients showed severe grammatical impairments, often performing at or near chance on language assessments. Yet their logical reasoning remained remarkably intact. They could infer hidden rules governing transformations of number sequences, solving 19/25 and 39/40 problems. They also excelled at nonverbal matrix reasoning, scoring 25/30 and 26/30—well above age-matched norms. The brain-imaging results pointed in the same direction. Neither inductive nor deductive reasoning substantially recruited the language network. The conclusion is powerful: natural language is not the medium of formal logical thought. Language allows us to communicate thoughts, but it is not necessarily the machinery that produces them. We can express understanding through language. But linguistic competence, by itself, is not evidence of understanding. I think it is crucial to keep this distinction in mind in an age in which fluent machines are increasingly mistaken for thinking machines. * Full paper in the first reply