In speech production, previously spoken and upcoming words can impinge on the word currently being said, resulting in perseverations (e.g., "beef needle soup" ) and anticipations (e.g., "cuff of coffee" ). These errors reveal the extent to which the language-production system is focused on the past, the present, and the future and therefore are informative about how the system deals with serial order. This article offers a functional analysis of serial order in language and develops a general formal model. The centerpiece of the model is a prediction that the fraction of serial-order errors that are anticipatory, as opposed to perseveratory, can be closely predicted by overall error rate. The lower the error rate, the more anticipatory the errors are, regardless of the factors influencing error rate. The model is successfully applied to experimental and natural error data dealing with the effects of practice, speech rate, individual differences, age, and brain damage.More than 45 years ago, Lashley ( 1951 ) directed the attention of psychologists to the problem of serial order. Ordered behavior, he wrote, cannot simply be the product of associations between elementary responses. Instead, there must be a hierarchically organized plan or schema that is separate from the responses and yet determines their order. Although it took some time for Lashley's paper to be appreciated (Bruce, 1994), his insights are now acknowledged to be central to theory in memory (e.g., Murdock, 1974), psycholinguisties (e.g., Levelt, 1989;MacKay, 1987), and motor control (e.g., Rosenbaum, 1990).This article examines the nature of order schemata in that behavior in which the serial-ordering problems are perhaps most acute, in language. We begin by reviewing evidence from serialorder errors in speech, particularly errors in which sounds or words are either anticipated, spoken ahead of their time, or perseverated, produced later than they should be. This evidence suggests that the past and future often impinge on the present while we are speaking and that the extent to which the languageproduction system is focused on the past or the future depends on a number of factors.We then present an experimental study of one of these factors, Gary S. Dell and Lisa K. Burger, Beckman Institute, University of Illinois at Urbana-Champaign; William R. Svec, Department of Psychology, Indiana University Bloomington.This research was supported by National Science Foundation Grant SBR 93-19368 and National Institutes of Health Grants DC-00191 and HD 21011 and grew out of a project involving Gary S. Dell, Myrna Schwartz, Eleanor Saffran, and Nadine Martin.We are grateful for the advice of David Adams, Howard Berenbaum, Gary Bradshaw, Kay Bock, Cooper Cutting, Vic Ferreira, Zenzi Griffin, Susan Garnsey, Anita Govindjee, Prahlad Gupta, John Huitema, Gordon Logan, Gregory Murphy, Neal Pearlmutter, Brian Ross, Christine Sevald, and Ulrich Schade and for the contributions of Linda May, Julie Owles, and the Beckman Institute.Correspondence concerning this article ...