Grammatical gender is independent of biological sex for the majority of animal names (e.g., a male giraffe is grammatically treated as feminine). However, there is apparent semantic motivation for grammatical gender classes, especially in mapping human terms to gender classes. This research investigated whether this apparent motivation in mapping between grammar and biological sex affects deductive inference in German speakers. We identified two contexts in which speakers unconsciously over-generalize the grammar-semantics mapping to make inappropriate deductive inferences about sex-specific biological properties. They tended to erroneously accept deductions when the sex in the premise and the grammatical gender of the target animal agreed. The sex-gender agreement affected the inference even when the sex of the target was explicitly indicated (e.g., die[FEM] männliche (male) Giraffe). Experiment 2 further suggested that these effects occur only when the gender-marking article accompanied the noun. Implications of the results for lintuistic relativity is discussed.