The purpose of this chapter is to provide a conceptual framework–the generic error-modelling system (GEMS)–within which to locate the origins of the basic human error types. This structure is derived in large part from Rasmussen's skill-rule-knowledge classification of human performance (outlined in Chapter 2), and yields three basic error types:

In particular, GEMS seeks to integrate two hitherto distinct areas of error research: (a) slips and lapses, in which actions deviate from current intention due to execution failures and/or storage failures (see Reason, 1979,1984a,b; Reason & Mycielska, 1982; Norman, 1981; Norman & Shallice, 1980); and (b) mistakes, in which the actions may run according to plan, but where the plan is inadequate to achieve its desired outcome (Simon, 1957, 1983; Wason & Johnson-Laird, 1972; Rasmussen & Jensen, 1974; Nisbett & Ross, 1980; Rouse, 1981; Hunt & Rouse, 1984; Kahneman, Slovic & Tversky, 1982; Evans, 1983).

The chapter begins by explaining why the simple slips/mistakes distinction (outlined in Chapter 1) is not sufficient to capture all of the basic error types. The evidence demands that mistakes be divided into at least two kinds: rulebased mistakes and knowledge-based mistakes. The three error types (skillbased slips and lapses, rule-based mistakes and knowledge-based mistakes) maybe differentiated by a variety of processing, representational and task-related factors, as discussed in Section 2.

Human error is a very large subject, quite as extensive as that covered by the term human performance. But these daunting proportions can be reduced in at least two ways. The topic can be treated in a broad but shallow fashion, aiming at a wide though superficial coverage of many well-documented error types. Or, an attempt can be made to carve out a narrow but relatively deep slice, trading comprehensiveness for a chance to get at some of the more general principles of error production. I have tried to achieve the latter.

The book is written with a mixed readership in mind: cognitive psychologists, human factors professionals, safety managers and reliability engineers – and, of course, their students. As far as possible, I have tried to make both the theoretical and the practical aspects of the book accessible to all. In other words, it presumes little in the way of prior specialist knowledge of either kind. Although some familiarity with the way psychologists think, write and handle evidence is clearly an advantage, it is not a necessary qualification for tackling the book. Nor, for that matter, should an unfamiliarity with high-technology systems deter psychologists from reading the last two chapters.

Errors mean different things to different people. For cognitive theorists, they offer important clues to the covert control processes underlying routine human action. To applied practitioners, they remain the main threat to the safe operation of high-risk technologies.

This chapter examines some significant contributions to the study of human error. Its primary aim is to outline the major influences upon the arguments presented later in this book, particularly in Chapters 3 to 5. But I also hope that it will convey something of the current state of cognitive theorising to those readers who are not themselves working in this field.

The first part of the chapter attempts to provide a modest historical vantage point from which to view contemporary treatments of error. It is necessarily selective because a complete account would encompass the entire history of psychological ideas. For our purposes, however, it is sufficient to consider the major influences of the past hundred years.

The second part deals mainly with the resource-limited aspects of human cognition: attention and ‘primary’ (or short-term) memory. This work has largely been carried out in the laboratory within the natural science tradition of experimental psychology. As such, the material discussed in these sections bears the characteristic hallmarks of this mode of investigation: a restricted focus upon well-defined, manipulable phenomena; limited, data-bound models and an abiding concern with resolving differences between theoretical contenders on the basis of their predictive performance.

The third part is concerned with the representation and deployment of stored knowledge and with the vast ‘community’ of specialist processors governing the more automatic aspects of perception, thought and action. Much of this work has been carried out within the more recent cognitive science tradition.

This chapter sketches out one possible answer to the following question: What kind of information-handling device could operate correctly for most of the time, but also produce the occasional wrong responses characteristic of human behaviour? Of special interest are those error forms that recur so often that any adequate model of human action must explain not only correct performance, but also these more predictable varieties of fallibility.

Most of the component parts of this ‘machine’ have been discussed at earlier points in this book. The purpose of this chapter is to assemble them in a concise and internally consistent fashion.

It is called a ‘fallible machine’ rather than a theoretical framework because it is expressed in a potentially computable form. That is, it borrows from Artificial Intelligence (AI) the aim of making an information-handling machine do “the sorts of things that are done by human minds” (Boden, 1987, p. 48). As Boden (1987, p. 48) indicates, the advantages of this approach are twofold: “First, it enables one to express richly structured psychological theories in a rigorous fashion (for everything in the program has to be precisely specified, and all its operations have to be made explicit); and secondly, it forces one to suggest specific hypotheses about precisely how a psychological change can come about.”

The description of the ‘fallible machine’ is in two parts. In the first seven sections of the chapter, it is presented in a notional, nonprogrammatic form.

So far, we have focused mainly upon the causes of errors, that is, upon the conditions that precede their occurrence and on the cognitive mechanisms that shape their more predictable forms. For the remaining chapters, the emphasis will shift towards their consequences, beginning here with a consideration of the processes involved in the detection and recovery of errors.

To err is human. No matter how well we come to understand the psychological antecedents of error or how sophisticated are the cognitive ‘prostheses’ – devices to aid memory or decision making–we eventually provide for those in high-risk occupations, errors will still occur. Errors are, as we have seen, the inevitable and usually acceptable price human beings have to pay for their remarkable ability to cope with very difficult informational tasks quickly and, more often than not, effectively. In conditions where “machines botch up, humans degrade gracefully” (Jordan, 1963). But, as we shall discuss further in the ensuing two chapters, the centralised supervisory control of complex, hazardous, opaque, tightly-coupled and incompletely understood technologies can, on occasions, transform these normally adaptive properties into dangerous liabilities.

If it is impossible to guarantee the elimination of errors, then we must discover more effective ways of mitigating their consequences in unforgiving situations. Many have suggested that this is really the only sensible way of combating the human error problem in high-risk technologies.

This book began by discussing the nature of human error and the theoretical influences that have shaped its study. It then proposed distinctions between error types based on performance levels and error forms derived from basic memory retrieval mechanisms. Chapters 4 and 5 presented a framework theory of error production, and Chapter 7 considered the various processes by which errors are detected. The preceding chapter examined some of the consequences of human error in high-risk technologies, looking in particular at the effects of latent failures.

It is clear from this summary that the bulk of the book has favoured theory rather than practice. This concluding chapter seeks to redress the balance somewhat by focusing upon remedial possibilities. It reviews both what has been done and what might be done to minimise the often terrible costs of human failures in potentially hazardous environments. More specifically, it deals with the various techniques employed or proposed by human reliability specialists to assess and to reduce the risks associated with human error.

The chapter has been written with two kinds of reader in mind: psychologists who are unfamiliar with the methods of human reliability analysis (not unsurprisingly since most of this material is published outside the conventional psychological literature), and safety practitioners of one sort or another. For the sake of the former, I have tried to make clear the model and assumptions underlying each technique.

This commentary had its origin in the Greek beginners' class at St Andrews, and was intended at the outset as a primarily linguistic aid to speech 1 in samizdat edition. However, early on in the project it occurred to me that a conventionally produced commentary on a selection of Lysias' works might be of interest to a wider audience. The broadly favourable reception of the Carey-Reid Demosthenes commentary suggested that a companion volume at the same level would be appropriate. In the mean time Usher's translation, with commentary, of a selection from Lysias (including one of the speeches in this volume, speech 1) and Scodel's commentary on 1 and 3, offering the level of linguistic support intended in my original project, have appeared. I believe that the difference of approach in the present volume will justify the limited overlap with these two works.

As with the Demosthenes volume, the emphasis in this commentary is primarily literary, though attention has been given to linguistic and textual problems where relevant. I have also sought to use the speeches to illustrate aspects of Athenian law, legal procedure and society. As with the Demosthenes volume, I have approached the speeches as devil's advocate, seeking the weak points in each speaker's case. With this approach there is obviously a danger, to which I found myself succumbing on occasion, of deifying disbelief.

On the murder of Eratosthenes

Date

There is no internal or external evidence to enable us to date the speech precisely.

The case

Athenian law on adultery was both broader and more severe than in most modern societies; broader in that the term moicheia, which is usually translated ‘adultery’, was applied to unauthorized sex (excluding rape) with the free female dependants of another man; more severe in that the law allowed a man considerable powers against anyone he caught committing moicheia with a woman under his control and protection, including (in the case of wife, mother, sister, daughter, or free mistress) the right to kill. These differences reflect a significant difference between the Greek view of the offence and our own. For us adultery, though recognized as an impropriety under divorce law, is a private matter between the individuals involved. For the Greeks the offence threatened the family, since it created a risk that an adulterine bastard might be introduced into it, with the result that control of family property and cults might be passed outside the bloodline. Hence the application of the term moicheia beyond marital infidelity, and also the severity of Athenian law, which in this as in other areas recognized the importance of the family. The present speech was written for a certain Euphiletos, who exercised the extreme right against a young man named Eratosthenes.

LIFE

The ancient biographical tradition concerning Lysias is both clear and consistent. He was born in Athens in 459/8, the son of a resident alien of Syracusan origin named Kephalos. At fifteen he migrated (either with his two brothers or just his older brother, Polemarchos) to the colony of Thourior, where he stayed until ejected by the anti-Athenian faction there in the civil disturbance which followed the destruction of the Sicilian expedition, returning to Athens in 412/11. He died in his late seventies or early eighties.

However, many scholars have preferred a later date for Lysias' birth. The traditional date would place his period of artistic activity (403– c. 380) between the ages of 56 and 78; this is not impossible, but it would certainly be unusual. Moreover, at Dem. 59.21–2, Lysias is mentioned as having both a mistress and a mother who is still alive, at a date which is unlikely to be earlier than 390 and may be as late as 380. This would make Lysias almost seventy at least, and his mother at least in her mid-eighties. Since longevity and sexual potency, like literary activity, are variables we cannot rule out this possibility; but again a later date for the birth would be more plausible. But since the tradition that Isokrates, born in 436, was younger by a significant margin than Lysias goes back to a contemporary source, we cannot plausibly bring Lysias' birth down beyond the mid-440s.

FILMER, LOCKE AND HOBBES. ‘TWO TREATISES’ AND CONTEMPORARY POLITICAL WRITING

If Locke wrote his book as a refutation of Sir Robert Filmer, then he cannot have written it as a refutation of Thomas Hobbes. It is almost as mistaken to suppose that he was arguing deliberately against Leviathan as to believe that he wrote to rationalize the Revolution. There would have been no point whatsoever for the intellectual champion of the Whig exclusionists to produce one more criticism of Hobbes. Professor Skinner has demonstrated that Hobbes did have an intellectual context and a following: he did not spring from nowhere and exist without effect, excepton his opponents. But he was politically the least important of all the absolutist writers. Filmer, on the other hand, was the man of the moment, a formidable and growing force with those whose political opinions mattered, and representing in himself the ipsissima verba of the established order. Therefore Locke found himself impelled to write on this subject, and for that reason Filmer's thinking lies directly behind his political doctrines. Moreover, his controversy with patriarchalism has a fundamental significance in the history of political and social thinking, for the development of the structure of modern society.

Locke rejected Hobbesian absolutism along with Filmer's, of course: the word ‘Leviathan’ occurs in his Second Treatise, and there are phrases and whole arguments which recall the Hobbesian position, and must have been intended in some sense as comments upon them.

‘Property I have nowhere found more clearly explained, than in a book entitled, Two Treatises of Government.’ This remark was made by John Locke in 1703, not much more than a year before he died. It must be a rare thing for an author to recommend one of his own works as a guide to a young gentleman anxious to acquire ‘an insight into the constitution of the government, and real interest of his country’. It must be even rarer for a man who was prepared to do this, to range his own book alongside Aristotle's Politics and Hooker's Ecclesiastical Polity, to write as if the work were written by somebody else, somebody whom he did not know. Perhaps it is unique in a private letter to a relative. What could possibly be the point of concealing this thing, from a man who probably knew it already?

Odd as it is, this statement of Locke anticipates the judgement of posterity. It was not long before it was universally recognized that Locke on Government did belong in the same class as Aristotle's Politics, and we still think of it as a book about property, in recent years especially. It has been printed over a hundred times since the 1st edition appeared with the date 1690 on the title-page. It has been translated into French, German, Italian, Russian, Spanish, Swedish, Norwegian, Hebrew, Arabic, Japanese and Hindi: probably into other languages too.

Whilst he was waiting at Rotterdam for a ship to take him home after the Revolution, Locke received the following letter from The Hague:

The writer was Lady Mordaunt, wife of his friend who was to become Earl of Monmouth and Earl of Peterborough and who was already in England with William III. The Convention she mentions was the Convention Parliament, then working out the constitutional future of England after James II had sputtered out. By 11 February Locke was in London: on the 12th the Declaration of Right was completed: on the 13th William and Mary were offered the crown.

This letter, except perhaps for its last phrase, aptly expresses the traditional view of the reasons why Locke sat down to write Two Treatises of Government. What was wanted was an argument, along with a scheme of government, an argument deep in its analysis and theoretical, even philosophical, in its premises, but cogent and convincing in its expression.