The classification of verbs as regular or irregular is to some extent a subjective matter. Sometimes the result of french irregular verbs list pdf conditional and selective historical sound changes is to leave certain words following a practically unpredictable pattern.
A language may have more than one regular conjugation pattern. A verb which does not follow the expected pattern based on the form of its infinitive is considered irregular. To some extent it may be a matter of convention or subjective preference to state whether a verb is regular or irregular. While examples of verbs irregular in spelling only are rare in English, they may be very common in other languages.
20th-century linguists revolved around whether small children learn all verb forms as separate pieces of vocabulary or whether they deduce forms by the application of rules. A common error for small children is to conjugate irregular verbs as though they were regular, which is taken as evidence that we learn and process our native language partly by the application of rules, rather than, as some earlier scholarship had postulated, solely by learning the forms. In fact, children often use the most common irregular verbs correctly in their earliest utterances but then switch to incorrect regular forms for a time when they begin to operate systematically. That allows a fairly precise analysis of the phases of this aspect of first language acquisition. When languages are being compared informally, one of the few quantitative statistics which are sometimes cited is the number of irregular verbs.