There is no knowledge of more frequent use than that, of duties and impost, whether customs paid at the ports, or excises levied upon the manufacturer.  Much of the prosperity of a trading nation depends upon duties properly apportioned; so that what is necessary may continue cheap, and what is of use only to luxury may, in some measure, atone to the publick for the mischief done to individuals.  Duties may often be so regulated as to become useful even to those that pay them; and they may be, likewise, so unequally imposed as to discourage honesty, and depress industry, and give temptation to fraud and unlawful practices.

To teach all this is the design of the Commercial Dictionary; which, though immediately and primarily written for the merchants, will be of use to every man of business or curiosity.  There is no man who is not, in some degree, a merchant, who has not something to buy and something to sell, and who does not, therefore, want such instructions as may teach him the true value of possessions or commodities.

The descriptions of the productions of the earth and water, which this volume will contain, may be equally pleasing and useful to the speculatist with any other natural history; and the accounts of various manufactures will constitute no contemptible body of experimental philosophy.  The descriptions of ports and cities may instruct the geographer, as well as if they were found in books appropriated only to his own science; and the doctrines of funds, insurances, currency, monopolies, exchanges, and duties, is so necessary to the politician, that without it he can be of no use either in the council or the senate, nor can speak or think justly either on war or trade.

We, therefore, hope that we shall not repent the labour of compiling this work; nor flatter ourselves unreasonably, in predicting a favourable reception to a book which no condition of life can render useless, which may contribute to the advantage of all that make or receive laws, of all that buy or sell, of all that wish to keep or improve their possessions, of all that desire to be rich, and all that desire to be wise[2].

FOOTNOTES: 

[1] A new Dictionary of Trade and Commerce, compiled from the
    information of the most eminent merchants, and from the works of the
    best writers on commercial subjects in all languages, by Mr. Rolt. 
    Folio, 1757.

[2] Of this preface, Mr. Boswell informs us that Dr. Johnson said he
    never saw Rolt, and never read the book.  “The booksellers wanted a
    preface to a dictionary of trade and commerce.  I knew very well what
    such a dictionary should be, and I wrote a preface accordingly.” 
    This may be believed; but the book is a most wretched farrago of
    articles plundered without acknowledgment, or judgment, which,
    indeed, was the case with most of Rolt’s compilations.