Bright and Burton (1994) demonstrated that, when subjects are shown a series of clocks in an incidental learning task, they become sensitive to regularities within these stimuli. If clocks consistently show times between 06:00 and 12:00, subjects show a later selection preference for new clocks conforming to the same constraints. Furthermore, the effect persists whether clocks are represented in analog or digital format, and regardless of whether the format changes between learning and test. The experiments reported here describe the effects of a radical context change in the apparent meaning of stimuli learned in an incidental fashion. The same numbers (e.g. 1145) were taught to subjects as either clock times or as telephone numbers. If interpreted as clock times, these numbers conform to a particular regularity. In four experiments we show that selection preference for rule-conforming items is only present if the subjects originally encode the numbers as clock times. We argue that abstraction of the regularity occurs during encoding rather than during retrieval and that the context in which this abstraction takes place critically determines classification performance.