About: Three-letter rule

In English spelling, the three-letter rule, or short-word rule, is the observation that one- and two-letter words tend to be function words such as I, at, he, if, of, or, etc. As a consequence of the rule, "content words" tend to have at least three letters. In particular, content words containing fewer than three phonemes may be augmented with letters which are phonetically redundant, such as ebb, add, egg, inn, bee, awe, buy, owe, etc. Vivian Cook says of the rule, "People who are told about it are often surprised that they were previously unaware of something so obvious."