Recent theories of speech production have sought to explain speech errors in terms of the permutation or decay of intended elements. More venerable accounts - Freud, Meringer and Mayer - on the other hand, acknowl- edged the influence of unintended elements on the occurrence and nature of errors, and offered data whose most plausible explanation seemed to be in terms of the effects of unintended material. In this paper, I re-examine the claims made by these authors, along with modern attempts to explain away their problematic data. Recent theories are also committed to a strict sequence of processing stages, but a closer examination of both modern and older corpora reveals an improbable proportion of errors caused, apparently, by the malfunction of two or more theoretically independent stages. There seems to be no way of naturally extending strictly sequential models to accommodate these data, and the sketch of an alternative is proposed in which strict sequence is replaced by parallel processes with checking.