In the prototonic form (after two proclitics), the root was unstressed and thus the root vowel was also deleted, leaving only the first consonant.

According to his own account, upon getting up one morning, he was puzzled by the question why the Gothic words fadar and broþar have different consonants after the root vowel.

Second perfect, which adds no suffix, but may modify the root vowel (into the o-grade of Indo-European ablaut).

Changes to the root vowel sometimes happen, as well.

Third conjugation words ending in n, g, or k have a u for their past participles' root vowel.

The nominative and accusative neuter singular ends in -t when the word's root vowel is short, and -tt when long.

Preference was given to "broad" rather than "narrow" root vowels, e.g., "mellom" rather than "millom"

The first assumption is that in pairs like bolbér/buélbe the root vowels were originally the same.

Note that whether the root vowel is "closed" or "open" affects the conjugation of the verb.

A final root vowel gets deleted before a suffix starting with a non-consonant.