Three letter rule

In English, the three letter rule (or short word rule) is the observation that content words are three letters long at least.
One- and two-letter words are mostly function words. Examples: "I", "at", "he", "if", "of", "or", etc. Therefore, content words almost all have at least three letters. Notice that content words with fewer than three phonemes get an extra letter or letters which are "phonetically redundant": the extra letters do not change the sound. Examples are such as "ebb, "add, "egg, "inn, "bee, "awe, "buy", "owe", etc.