Is human thought fully embedded in language, or do some forms of thought operate independently? To directly address this issue, we focus on inference-making, a central feature of human cognition. In a 3T fMRI study we compare logical inferences relying on sentential connectives (e.g., not, or, if . . . then) to linguistic inferences based on syntactic transformation of sentences involving ditransitive verbs (e.g., give, say, take). When contrasted with matched grammaticality judgments, logic inference alone recruited ''core'' regions of deduction [Brodmann area (BA) 10p and 8m], whereas linguistic inference alone recruited perisylvian regions of linguistic competence, among others (BA 21, 22, 37, 39, 44, and 45 and caudate). In addition, the two inferences commonly recruited a set of general ''support'' areas in frontoparietal cortex (BA 6, 7, 8, 40, and 47). The results indicate that logical inference is not embedded in natural language and confirm the relative modularity of linguistic processes.fMRI ͉ logic ͉ reasoning ͉ semantics ͉ syntax T he interplay between language and thought is pivotal to the study of human cognition (1-4). A principal issue is the extent to which thinking is embedded in language (5, 6). Within neuroscience, the matter has been explored in the domain of arithmetic (7), music (8), theory of mind (9), and deductive reasoning (10, 11). In the case of deduction, however, the evidence is highly contradictory. Some studies report that logic inference recruits neural structures traditionally engaged by linguistic processing (10, 12). These findings would suggest that thought is deeply rooted in language, a view consistent with certain psychological and philosophical perspectives on deduction (13,14). Other studies have failed to detect such activity (15, 16), which counts against the hypothesis that reasoning is tributary to language. These competing interpretations, however, are entirely based on indirect secondary observation qualitatively comparing language activations in one study to logic activations in another study across different methods, materials, paradigms, and subjects. In the present study we address this issue directly by comparing, within the same group of participants, inference based on logic connectives to inferences based on the syntax and semantics of ditransitive verbs.Consider, for example, arguments 1a and 2a in Table 1 (each with a single premise). The two arguments are equally valid in the sense that the truth of their respective premises guarantees the truth of their conclusions. But their validity rests on vocabulary from different lexical categories. The validity of argument 1a is based on the sentential connectives ''if . . . then,'' ''or,'' etc., whereas the validity of argument 2a depends on the principal phrasal verb (and similarly for the invalidity of arguments 1b and 2b, respectively). The semantic contrast between the two cases is apparent although difficult to characterize precisely (17). Roughly, connectives do not contribute to the topic of a sentence a...