A Technique for Computer Detection and Correction of Spelling Errors
Damerau, F. J.
Commun. ACM, 7(3) 171-176 (1964) [pdf]
The method described assumes that a word which cannot be found in a dictionary has at most one error, which might be a wrong, missing or extra letter or a single transposition. The unidentified input word is compared to the dictionary again, testing each time to see if the words match—assuming one of these errors occurred. During a test run on garbled text, correct identifications were made for over 95 percent of these error types.