English language

Irregular verbs are verbs that don’t take on the regular –d, -ed, or -ied spelling patterns of the past simple. – “[I]rregular verbs . . . derive from the Old English period. At that time they were called strong and weak verbs respectively. Strong verbs formed their past tense and past participle with an ablaut or vowel gradation. Weak verbs formed their past tense and past participle with an inflentional suffix, that is, a {-d} or {-t} suffix. With the loss of inflections during the Middle English period, all new verbs took on the weak verb formation with an {-ed} or {-t} in past forms. This weak formation soon became the norm for what we now refer to as English regular verbs; strong verbs became irregular verbs.” (Bernard O’Dwyer, Modern English Structures, 2nd ed. Broadview Press, 2006)

According to the Longman Student Grammar (2002), the nine most common lexical verbs in English are all irregular: say, get, go, know, think, see, make, come, and take. Here is a list-of-irregular-verbs.