Spell check is a function which is available on many computers. It allows users to scan a document for words which have been misspelled. Most word processing programs have a built in spell check function, and it is possible to find spell checks which can be integrated into instant messaging programs, web browsers, and other types of programs. Having spell check isn't quite a replacement for a real human editor, but it can help people catch basic spelling mistakes so that their communications are more presentable.
The earliest spell check programs simply scanned documents for words they didn't recognize, and alerted users to the fact that something was spelled incorrectly, without providing any suggestions for alternate spellings. These systems were eventually replaced by spell checks which generated a list of possible words for the user to select from to replace the misspelled word. If, for example, a user typed “thru,” the spell check program might suggest “threw” or “through” as possible alternatives. These programs also allow users to add exceptions to the program's dictionary.
One of the major problems with a spell check program is that it cannot catch homophone errors, and users can also generate homophone errors by accident if they are unfamiliar with the language. In the example above, the user might have written “I went thru the door,” and select “threw” as a replacement rather than “through,” not realizing that he or she has made a mistake. Especially for people who really struggle with spelling, the computer's list of suggestions may not match the user's intention at all. If, for instance, a user typed “She was very thru about checking my work,” the computer would be unlikely to suggest “thorough,” the correct word, as a replacement for the misspelled word.
Some people have attempted to remedy the homophone problem by developing more sophisticated spell check applications which read words in context instead of just looking for words which are not spelled properly. These programs can catch some homophone errors, and they will also avoid suggesting multiple homophones for one misspelling, making it more likely that the user will select the word he or she intends to use. These programs learn from use, which means that each generation will be better than the previous one.
Some people have criticized the widespread use of spell check utilities, arguing that they make people lazier, as people assume that misspellings can be corrected, rather than learning to spell words properly or learning to identify homophone errors. These people theorize that the state of written communications has been weakened by the use of spell check programs. However, others have argued that using a spell check can make people feel more comfortable while they are learning a new language, and that everyone can make slips of the keyboard and spelling mistakes which they might not readily identify without some help, since it is often hard to catch errors in one's own work.