The dictionaries with which most people are familiar list, in varying degrees of comprehensiveness, the words in a language, providing their standard and alternative spellings and definitions. There is a general perception among the public that dictionaries should be authoritative guides to language. This view holds that the spellings and usages contained in a dictionary are correct, and that those that are not are incorrect. Therefore, if a slang locution such as “ain’t” is not listed in a dictionary, it should not be used.
The earliest English language dictionaries often veered toward a kind of whimsicality that reflected the backgrounds and prejudices of their compilers. Samuel Johnson’s A Dictionary of the English Language (1755), for example, defined “oats” as “a grain that in England is generally fed to horses, but in Scotland supports the people.” Variant spellings were more common and more widely tolerated before the eighteenth century than they were after it, largely because of increased public literacy and the proliferation of standardized spellings in printed material.
In addition to the general, word-definition dictionaries with which most people are familiar, specialized dictionaries exist that focus on specific vocational or other areas. Some dictionaries emphasize such aspects of language as etymology, pronunciation, dialects, or synonyms and antonyms. Others offer such encyclopedic information as that found in biographical or geographical dictionaries. Still others provide bilingual equivalencies for non- native speakers of a language, such as those found in bilingual dictionaries.