In Latin, most verbs have four principal parts. For example, the verb for "to carry" is given as portō – portāre – portāvī – portātum, where portō is the first-person singular present active indicative ("I carry"), portāre is the present active infinitive ("to carry"), portāvī is the first-person singular perfect active indicative ("I carried"), and portātum is the neuter supine. Most of the verb forms in Latin derive from the first two principal parts: portābō, "I shall carry", is derived from the root portā-, taken from the present infinitive. However, all active perfect forms are derived from the third principal part (so portāveram, "I had carried", is taken from portāv-) while the perfect participle (portātus, portāta, portātum, "having been carried") is derived from the supine and is used to form perfect passive participle with the auxiliary verb sum (such as portātum est, "it has been carried"). The auxiliary verb is often dropped when writing poetry in Latin.
For many Latin verbs, the principal parts are predictable: portō shown above uses a single stem, port-, and all principal parts are derived from them with the endings -ō – -āre – -āvī – -ātum. Others have more complicated forms: regō ("I rule") has 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.