Shaw and Tipper in their bibliography and guide argue that directories are ‘one of the most frequently used sources within historical studies’.  If so, the accuracy of the source is of primary importance. This article will examine this issue, starting with the development of historians’ interest in directories, considering some of the uses to which they have been put and assessing a view that directories can be more trouble than they are worth. It will argue that directories, translated into machine-readable form, offer a superb historical source, particularly to the growing numbers of computer-literate local historians.
The best introduction to the use of business directories (of any period) as a historical source is supplied by Norton in her guide to pre-1856 directories. She modestly points out that her book is ‘not a complete bibliography, but a guide to directories’ , recognising the impossibility of an exhaustive survey of such a range of often-ephemeral publications. Demonstrating a real empathy with the compilers of the early directories, she examines the publications from a purchaser’s viewpoint, avoiding the anachronistic fallacy of considering them purely as a historical source. She notes, ‘Directories are, by nature and origin, instruments of commerce they are a means of communication, essential to extensive trade relations and a wide market and they were compiled to meet the commercial need of easy and rapid intercourse between buyer and seller … The distinguishing characteristic of the directory is that its purpose is commercial.’  They supply lists of names and addresses as valuable to modern historians as they were to their intended users: Norton quotes approvingly the words of John Ferrar who compiled a directory of Limerick in 1769, ‘This Pamphlet will appear at first view trifling to some but it will shew the present state and constitution of this City better perhaps than a voluminous history. ‘ 
There are dangers for the unwary: the compilers of these lists are frequently prone to error. Norton includes a necessary caveat, ‘It would be misleading to regard [directories] as either precise or accurate. A glance at any two directories of the same place for the same year will reveal disconcerting differences and there are plenty of examples of dishonesty among directory compilers …’  Such dangers can be guarded against by checking other sources. Loyal purchasers suggest reliability – a directory had to retain their confidence to continue in print, as Norton recognises, ‘In general, when a directory is printed and published in its own locality part of a series appearing regularly over a number of years, it can be expected, prima facie, to be reasonably reliable.’ 
Norton ends her survey in 1856, from which point Shaw and Tipper supply an extensive, but not exhaustive list of later directories. More fortunate than Norton, they could call on the work of libraries and local history societies who had begun to produce their own bibliographies of directories. Lancashire is particularly well-served in having the Tupling and Horrocks bibliography : ‘Perhaps the most comprehensive of these local guides are those for Lancashire and Staffordshire’. 
Turning next to the use to which directories can be put, Oliver demonstrates that without directory evidence whole areas of urban life would be impossible to recapture. Such evidence enabled him to map the ‘dispersal of furniture-making undertakings from the East End of London to the Lea Valley’.  More cautiously, Davies, Giggs and Herbert flag up ‘the critical need for comparability among urban studies … Individual studies cannot be adequately compared until the information sources as well as the analytical techniques used are known to be reliable and capable of cross-comparison. Thus, generality and comparability are judged to be more important than the need to provide individualized and unique analyses’.  Nowhere is this truer than in the use of directories. The authors note, ‘The compilation of a directory is essentially a private matter so it is not surprising that errors of omission occur … an uncritical use of the source can lead to serious errors.’ Researchers ignore their warning at their peril, ‘Although these points may appear rather trite to the casual observer, in total they can contribute a 5 or 10 per cent error in the number of commercial premises attributed to settlements in any count of functions’.  Some of the critics considered below argue that the margin of error is far wider.
The use of directories by historians was considered in a series of articles in the Local Historian beginning in 1975 when Duggan warns that the earlier directories are ‘far from complete and best used only to judge wide shifts in magnitude and trend’.  Page, in his study of Ashby-de-la-Zouch, has more confidence in his directories: in Drake’s directory of 1862, ‘There are some inaccuracies, but over ninety per cent of the Ashby people he mentioned can be traced to the 1861 Census and many of the others were probably only absent from the town on that night’.  He compares two directories with the corresponding Census returns for the area and notes that, ‘The Census shows that over one third of the householders of Ashby were engaged in crafts in 1861 and only one sixth in trades. Both directories reverse this order …’, which leads him to conclude, ‘directories are of much more use as an indicator of the socio-economic structure of a market town than they are for plotting the pattern of occupations’.  Wilde, in a study of the south-west Pennines silk industry, found ‘… business directories are one of the few comprehensive and comparative sources for the period of rapid industrialization during the first three decades of the nineteenth century … Despite problems of interpretation, these directories give an invaluable perspective on the growth and changing structure of the … silk industries in this crucial period [and] yield interesting information, virtually unobtainable from any other source …’ 
Geoffrey Timmins provides a more focussed analysis of directory errors in his examination of the development of steel making in Sheffield. He found that ‘shortfalls of between ten and thirty per cent are usual’ in the classified list of steel makers.  This leads him to question directory evidence, ‘… local historians must ask searching questions before they can be satisfied that the number of producers they locate in trade directory lists give anything like a true picture’.  Walton believes Timmins comes close to ‘a fully articulated confession of a loss of faith’ in their usefulness and is even more forceful, arguing that ‘… the 17805 and 17905 was the period when trade information placed in directories was least to be trusted …’, and that, ‘… even in the nineteenth century, directories may exhibit a bias towards higher-status trades and traders …’  But both Timmins and Walton are in danger of throwing the baby out with the bathwater. When Walton warns against the exclusive use of directory evidence, surely he is only expressing an academic truism. His censure of high-status bias is anachronistic. The early directory compilers did not aim at census completeness: they listed those sections of society that supplied potential customers for their readers. As such, they supply an excellent insight into social gradations.
The sheer volume of the data available represents the major methodological difficulty (and potential value) in using directories. They are most comprehensive in their coverage of the larger urban centres, for which they can yield thousands of individual entries. How to handle such largesse? The task of manipulating vast amounts of data from different sources, differently categorised is daunting, especially since much material is still published in print form only. On-line versions can be found at the various commercial family history sites, but these seem to be better suited to searches for family histories rather than a town history. The University of Leicester some years ago created a ‘digital library of historical directories’ but it is no longer maintained: Lancashire directories available on the university site can be found at http://specialcollections.le.ac.uk/cdm/search/collection/p16445coll4/searchterm/Lancashire/field/place/mode/exact/conn/and/order/nosort