the perfect form rēxī and perfect participle rēctum, derived as *reg-sī and *reg-tum. A handful of verbs, such as sum - esse - fuī - futūrum ("to be") are simply irregular. A number of verbs have fewer than four principal parts: deponent verbs, such as hortŏr – hortāri – hortātus sum, "to exhort", lack a perfect form, as do semi-deponent verbs, such as audeō – audēre – ausus sum, "to dare"; in both cases, passive forms are treated as active, so all perfect forms are covered by the perfect participle. A handful of verbs are also defective, including the verb ōdī – ōdisse, "to hate", which only has perfect forms derived from a single stem. Ancient Greek Verbs in Ancient Greek have six principal parts: present (I), future (II), aorist (III), perfect (IV), perfect middle (V) and aorist passive (VI), each listed in its first-person singular form: Part I forms the entire present system, as well as the imperfect. Part II forms the future tense in the active and middle voices. Part III forms the aorist in the active and middle voices. Part IV forms the perfect and pluperfect in the active voice, and the (exceedingly rare) future perfect, active. Part V forms the perfect and pluperfect in the middle voice, and the (rare) future perfect, middle. Part VI forms the aorist and future in the passive voice. One principal part can sometimes be predicted from another, but not with any certainty. For some classes of verbs, however, all principal parts can be predicted given the first one. Germanic languages English Excluding four common irregular verbs, the principal parts of all other English verbs are the infinitive, preterite and past participle. All forms of these English verbs can be derived from the three principal parts. Four verbs have an unpredictable 3rd person singular form and the verb "to be" is so irregular it has seven separate forms. Lists or recitations of principal parts in English often omit the third principal part's auxiliary verb, rendering it identical to its grammatically distinct participial form. For example, the verb "to take" has the principal parts take–took–(have) taken. The verb "to bet" has bet–bet–(have) bet and the verb "to break" has break–broke–(have) broken. With irregular verbs the simple present 3S (he, she, it) is derived from infinitive+'s' with the exception of spelling changes such as: catch-catches, fly-flies and teach-teaches, which follow the same rules