In the second part of the twentieth century there began to be a marked increase in the number of reference books available in bookshops. No longer was the reference library of the average fairly educated household restricted to one dictionary, probably dog-eared and several decades old, one out-dated copy of Roget's Thesaurus, either much-thumbed or pristine, according to the needs of the household, and possibly an old copy of Fowler's English Usage. This increased interest in reference publishing started with dictionaries and a great variety of these, in various shapes and sizes, began to be made available to the public. This sparked off an interest in other kinds of reference books. Existing ones began to be regularly updated and a whole deluge of new ones appeared. These included thesauruses, guides to good usage, guides to good grammar, guides to correct spelling, hints on how to improve your writing, books of idioms and so on.