While his poetry and fiction, while excellent and well-received, are not often recognized as among the great works of his period, his contributions to the English language and the subject of literary criticism are immensely noteworthy. He is considered one of the greatest critics of all time, and his dictionary is still used today by scholars and writers. At the age of 25, after serving an apprenticeship with a London bookseller, Johnson started work as an editor at the Scottish publisher William Strahan. During this time, he produced "A Dictionary of the English Language" (1755), which has been called "the most ambitious, influential, and successful linguistic project of its time." The first edition of 5000 copies was sold out within a year of publication. It has been described as "a remarkable achievement for its age," and it remains in use today alongside more recent dictionaries. In addition to its importance in establishing good grammar and correct usage, the dictionary also marked a significant advance in the treatment of words in English. Before this time, words were defined simply by giving their origin (such as "connoting" or "derived from") or by listing their parts (such as "diachronic" meaning "of two different periods"). But Johnson changed all that with his approach, which focused on how words are used in sentences to convey meaning.