Judgements of grammatical acceptability were made for correct and reversed ‘Y if X’ and ‘If X, Y’ sentences. Children aged 4; 10–8; 7 judged sentences ‘sensible’ or ‘silly’ and modified the sentences to make them ‘silly’ or ‘sensible’. Children failed to differentiate correct and reversed-order sentences prior to age 7 or 8. There was no evidence of an order-of-mention response strategy, but ‘If X, Y’ and ‘If Y, X’ sentences were easier to judge than ‘Y if X’ and ‘X if Y’, suggesting that children prefer sentences in which stated order parallels temporal order. The strategies used to modify the sentences changed with age from content changes to order reversals. The modifications suggested that contingency becomes a component of the meaning of if before the child assigns unidirectional event order as a component of if.