Every language has areas where it clings to the established rules and areas where it breaks them every chance it gets. In English, verbs do both. Regular verbs are well behaved whether they are describing something that happened in the past, the present, or the future. They comply the same way every time with the rules of conjugation. Irregular verbs, however, are the bad boys of action words because they take unexpected forms when speaking of the past.
It’s impossible to determine the exact number of verbs in any language at any given moment. Languages are really very fluid; speakers can coin a verb or use one that hasn’t be officially recognized and captured by a dictionary, and a verb can also vanish from popular parlance. Given that, linguists estimate between 25,000 and 100,000 verbs in English, or about 15% of the lexicon, might be in daily use. Of these, a fluent speaker needs to have a handle on an irregular verb only once in a while — 400 of them are all that are required for fluency.
It’s tempting to assume from these figures that the irregular verb collection in English is not something speakers need to be overly familiar with. That’s not entirely true as among the most commonly used verbs is likely to be an irregular one. Where would we be, after all, without the verb to be? It is not only an irregular verb in the past but in the present as well. Other common irregular verbs include have, eat, and do.
While most irregular verbs are actually pretty well behaved in the present tense, wearing the same endings as their entirely regular cousins, the verb to be is an exception. I am, but you are, and she is. This sets it apart from other irregulars. For example, I run, you run, and they run, while she runs follows the rules for present tense conjugation.
Regular verbs form a pretty predictable past tense by slapping on the ed morpheme. The basic past tense uses the same form as the past participle: I walked to the store last night is a single action that is finished, and I have walked to the store every night this week is the same verbal form coupled with have, making it a past participle. Many an irregular verb is irregular only up to a point, and once they’ve established their irregular forms, it remains the same with the past participle. I sold my house and I have sold several houses use the same form.
Other irregular verbs turn rule breaking into a fine art. These are the verbs that insist upon an irregular conjugation in the past. I swore I would learn English is the basic past, whereas I have always sworn I would learn English employs the past participle.