English is a beautiful, messy, gloriously inconsistent language. We learn its quirks from a young age: one mouse, two mice; one goose, two geese; but one house, two houses? Why do we say I was, but we were? These aren’t random mistakes made by our ancestors. They are linguistic fossils, echoes of a time before English was even English. And one of the most fascinating culprits behind these stubborn irregularities is a lesser-known but crucial sound change: an ancient “glitch” in the system known as Verner’s Law.

To understand this glitch, we first have to look at the main program it was affecting: the famous Grimm’s Law.

The Main Program: Grimm’s Law Sets the Stage

Around 2,500 years ago, a group of dialects known as Proto-Germanic began to split off from their parent, Proto-Indo-European (the ancestor of most languages in Europe and the Indian subcontinent). This split was defined by a massive, systematic shift in consonant sounds, first described by Jacob Grimm (yes, one of the fairytale brothers).

Grimm’s Law explains why Germanic languages like English, German, and Dutch have different starting consonants for related words than non-Germanic languages like Latin, French, or Sanskrit. The changes were remarkably consistent. For example:

• A “p” sound in Proto-Indo-European (PIE) became an “f” sound in Proto-Germanic.
  • Latin: pater → English: father
  • Latin: piscis → English: fish
• A “t” sound became a “th” (written as þ) sound.
  • Latin: tres → English: three
• A “k” sound became an “h” sound.
  • Latin: cornu → English: horn

This was the “rule”. For decades, linguists thought it explained everything. But there were annoying exceptions they couldn’t figure out. Why, for instance, did the PIE word for “hundred”, *ḱm̥tóm*, give us the Latin centum (with a “k” sound) but the Gothic hund (with a “d”)? According to Grimm’s Law, the “t” should have become a “th” sound, not a “d” sound. It was a mystery that baffled the experts.

The Glitch in the Code: Enter Verner’s Law

The solution came in 1875 from a brilliant Danish linguist named Karl Verner. He noticed a pattern hidden in plain sight, a factor no one had considered: the original word’s stress accent in Proto-Indo-European.

Verner discovered that Grimm’s Law worked perfectly as long as the PIE stress fell on the syllable before the consonant in question. But if the stress came after the consonant, a “glitch” occurred. This glitch took the new, voiceless consonants created by Grimm’s Law (like f, th, h) and made them voiced.

Here’s the core of Verner’s Law:

If a voiceless fricative (*f, *þ, *h, *s) came immediately after an unstressed syllable in a Proto-Indo-European word, it became voiced (*b, *d, *g, *z).

Think of it as a software patch that only ran under a specific condition—the location of stress. This seemingly minor detail had massive consequences, and its ghost still haunts our grammar today.

The Ghost in the Grammar: “Was” and “Were”

The most stunning piece of evidence for Verner’s Law in Modern English is the verb “to be”. Why do we use was for the singular past, but were for the plural?

Both words come from the same PIE root, *wes-, meaning “to remain” or “to dwell”.

1. The story of “was”: In the singular forms (like “I was” or “he was”), the stress in PIE was on the root of the word: *wás-. The consonant *s was preceded by a stressed vowel. So, it was unaffected by Verner’s Law. It remained an *s sound, eventually giving us Old English wæs, and our Modern English was.
2. The story of “were”: In the plural forms (like “we were” or “they were”), the stress was on the ending, not the root: wes-ónt. Here, the *s sound was preceded by an unstressed vowel. This was the exact condition that triggered Verner’s Law!

So, the glitch activated:

• The *s became voiced, turning into a *z sound.
• Later, in the history of Old English and other Germanic languages, this *z sound systematically shifted to an *r sound (a process called rhotacism).

This ancient chain reaction—unstressed syllable → Verner’s Law (*s* to *z*) → Rhotacism (*z* to *r*)—is the direct reason we have the pair was and were. It’s a grammatical fossil, perfectly preserved.

You can see this same ghost in other word pairs, like lose and forlorn. Both derive from the same root. The past participle forlorn comes from Old English forloren. The stress was on the prefix (for-), leaving the root unstressed and triggering the *s → *z → *r shift.

What About “Mice” and “Geese”?

Now, you might be wondering about our original examples, mouse/mice and goose/geese. Are they also victims of Verner’s Law? The answer is no, but they are products of a similar kind of ancient, rule-based change.

These irregularities are caused by something called I-Mutation (or I-Umlaut). In Proto-Germanic, the plural of *mūs* (mouse) was *mūsiz*. The *i* sound in the plural ending “pulled” the vowel in the root of the word forward in the mouth, changing it from a back vowel (*ū*, like in “moose”) to a front vowel (*ȳ*, like in French “tu”).

• Singular: *mūs → Old English mūs → Modern English mouse
• Plural: *mūsiz → Old English mȳs → Modern English mice

The same thing happened to *fōt*/*fēt* (foot/feet) and *gōs*/*gēs* (goose/geese). The plural ending, long since vanished, left its “shadow” on the vowel of the word. So while Verner’s Law explains consonant irregularities, I-Mutation explains many of our vowel irregularities. Both show how forgotten bits of grammar can leave permanent marks.

A Living Linguistic Museum

Verner’s Law is a beautiful reminder that language isn’t just a tool we use; it’s a living artifact we inhabit. The words we speak every day are layered with history, carrying the echoes of forgotten accents and grammatical rules from thousands of years ago. The irregularities we stumble over aren’t errors; they are clues. They are the ghosts of a vanished sound system, glitches from an ancient time that make English the wonderfully weird and fascinating language it is today.