Why Does One Foot Become Two Feet? A Vowel Reached Forward for a Sound That Vanished

In the early Germanic languages a vowel in the ending of a word could pull the vowel of the stem towards it, because a speaker anticipating a front vowel begins moving the tongue forward while still producing the previous one. Where the ending contained an i or a j, the stem vowel shifted forward in the mouth. That would be an unremarkable piece of anticipation, except that the endings responsible were then weakened and lost entirely over the following centuries, leaving a stem vowel that had been altered by something no longer present in the word.

The results are the irregular plurals and pairs everybody learns as exceptions:

• •Foot and feet, tooth and teeth, goose and geese
• •Man and men, mouse and mice, louse and lice
• •Full and fill, blood and bleed, food and feed
• •Long and length, strong and strength, broad and breadth
• •Old and elder, gold and gild, whole and heal
• •Doom and deem, brood and breed

German writes the shifted vowels with two dots above the letter, and the mark has a specific history rather than being arbitrary. Scribes originally wrote a small letter e above the vowel to show the change, since the shifted sound was felt to be the original vowel coloured towards an e. In the handwriting of the period that small e was written as two short vertical strokes, and those strokes were progressively reduced to two dots in print. The mark therefore records a letter rather than a sound, which is why the same vowels can be written with an e after them instead where the mark is unavailable.

The same change ran through the whole Germanic family and left different residues in each language. Modern German marks it in writing and uses it productively, forming plurals, comparatives and diminutives by it, so a speaker applies it to new words without thinking. The Scandinavian languages carry it extensively and mark it with different letters, including the o with a stroke and the a with a ring. Dutch shows it in a reduced form. English lost the ability to apply it and retains only the fossil pairs, so an English speaker cannot form a new plural this way and must learn each survival individually, which is exactly why they are taught as irregularities.

The same two dots are used for a completely different purpose and confusing the two is common. A diaeresis, identical in appearance, indicates that two adjacent vowel letters are to be pronounced separately rather than as one sound, which is why it appears in names and in a small number of English words in conservative usage. That mark separates vowels, where the one discussed here marks a vowel that changed. A third use, purely decorative and adopted by rock bands from the 1970s, has no linguistic function at all and frequently sits on letters that could not carry the mark in any language that uses it.

A vowel in a word ending pulled the stem vowel forward in the mouth, then that ending weakened and disappeared, leaving the altered stem vowel with nothing in the word to account for it. English irregular plurals and pairs like full and fill are the residue. The German mark descends from a small letter e written above the vowel and reduced to two strokes in print.