Standard accounts of derivational morphology assume that it is incremental: some words are formed on the basis of others, and each derivational family has a base from which all of the other words are derived. The importance of the base has been questioned by paradigmatic approaches to morphology, which posit that word systems are about multidirectional relationships between words and paradigm cells, in which no word has a privileged status. This paper seeks to test which of these two views makes (...) more accurate predictions about speakers’ cognitive representations of derivational families. We perform an acceptability judgement experiment in which speakers are asked to evaluate the acceptability of a pseudoword conditional on another pseudoword in the same derivational family. We find that speakers are aware of implicative relationships between words in the same family, and that they opportunistically exploit probabilistic relationships between surface words, regardless of whether the base form is the predictor, the target of prediction, or not at all involved in the task. (shrink)