Many people know at least the outline of Johnson’s life: his birth on September 18, 1709, in Lichfield, Staffordshire; his studies at Oxford’s Pembroke College (which he left after about a year, without a degree); and his struggles to make a living as a writer in London.

These struggles were slightly eased when Robert Dodsley and a group of other publishers commissioned Johnson to compile an English dictionary.

As John Wain says in his biography of Johnson, “June 18, 1746, is the date that marks Johnson’s turning-point. From now on, he is no longer a hand-to-mouth hack-writer; he is subsidized by a group of responsible entrepreneurs”.

Johnson (often called Dr Johnson) optimistically thought that he could write the dictionary in three years but, even with help from about half-a-dozen assistants, the task took three times as long. This is par for the course in lexicography: most dictionaries take much longer than anticipated. When James Murray started work on the Oxford English Dictionary, it was intended to take ten years but it actually took 50.

Despite Johnson’s well-known jibes at Scotland, Boswell pointed out that most of his assistants were Scots. The assistants’ main task was to copy out the illustrative quotations that Johnson selected from books in which he underlined the chosen word in pencil and marked within brackets the quotations to illustrate those words.

Johnson's most famous jest about the Scottish was in his Dictionary’s definition of oats: “A grain, which in England is generally given to horses, but in Scotland supports the people”.

Boswell, himself a Scot, got his own back on Johnson when they visited Lichfield.

“Oat cakes . . . were served at breakfast. It was pleasant to me to find, that oats, the food of horses, were so much used as the food of the people in Dr Johnson’s own town”.

One of Johnson's greatest innovations was his use of illustrative quotations. They not only showed how words are actually used but helped to clarify for Johnson how to divide each word into separate senses. Being a staunch moralist, Johnson tended to choose quotations which contained an uplifting or educative message, or at least had literary merit.

Assembling the quotations confirmed for Johnson the difficulty of regularising the language. Already in the Plan he drew up in 1747, he had stated that “the chief intent . . . is to preserve the purity and ascertain the meaning of our English idiom”.

Yet he also recognised that “language is the work of man, of a being from whom permanence and stability cannot be derived”. When the Dictionary was finished, Johnson's Preface described the lexicographer as someone who does “not form, but register the language”. He realised that “every increase in knowledge . . . will produce new words, or combinations of words”.

Many previous pundits, including Defoe and Swift, hoped that English could be fixed in the way that the Académie Francaise tried to standardize French. Recognising that this is impossible, Johnson tended to adopt a ‘descriptive’ approach rather than being ‘prescriptive’ — and this principle has been at the heart of the best dictionaries ever since.

Nevertheless, Johnson’s self-opinionated tendencies made him feel that “every language has likewise its improprieties and absurdities, which it is the duty of the lexicographer to correct or proscribe”.

Johnson often shamelessly used the Dictionary to express his own opinions. His prejudices show in such definitions as Whig (“the name of a faction”), puritan (“a sectary pretending to eminent purity of religion”), and fortuneteller (“one who cheats common people by pretending to the knowledge of futurity”).

Johnson was a staunch High Church Anglican, as one can see in such definitions as “Bible, the sacred volume in which are contained the revelations of God”.

A freethinker is “a libertine; a contemner of religion”. He defines Methodist as “one of a new kind of puritans lately arisen, so called from their profession to live by rules and in constant method”.

His dislike of the French was evident in this definition: “Frenchify, to infect with the manner of France; to make a coxcomb”. And he calls ruse “a French word neither elegant nor necessary”.

This subjective viewpoint actually helps to humanise the book. Although Boswell’s Life of Johnson gives a vivid picture of the man, the Dictionary also shows us much of his personality.

The preface describes rather movingly the difficulties involved in writing a dictionary and the personal problems he faced while compiling it. His definition of lexicographer as “a harmless drudge” is well-known (although the full definition is “A writer of dictionaries; a harmless drudge, that busies himself in tracing the original, and detailing the signification of words”). He defines one sense of dull as “not exhilarating; not delightful; as, to make dictionaries is dull work”.

Yet Johnson’s Dictionary is anything but dull — something I shall say more about next month.

Tony Augarde is the author of The Oxford Guide to Word Games (OUP, £14.99) and The Oxford A to Z of Word Games (OUP, £4.99).