An experiment is reported which tests psycholinguistic hypotheses about conditional rules of the form ‘If p then q’ (IT) and ‘p only if q’ (OI). It is postulated that each rule has a ‘directionality’ determined by linguistic usage which is ‘forwards’ for IT rules and ‘backwards’ for OI rules. It is further suggested that where temporal relations exist between the events denoted by p and q, the rules will be understood and processed more rapidly if the directionality of the rule is congruent with the temporal order. The results supported these hypotheses and provide a useful replication and extension of previous work.