Psychological investigations of deductive reasoning focus on inferences drawn from premises conveying operators such as if, and, or, and not, and quantifier terms such as all and some. Formal logic typically is usedtheories to determine which deductive inferences are valid. People routinely draw many valid inferences, but often accept others that are fallacious, and psychological research needs to account for both. Some researchers, such as Jonathan Evans, have focused on task features that influence fallacious inferences, proposing biases and heuristics in reasoning. This approach, however, does not explain the valid inferences that people make, nor the ...