In language learning, the principal parts of a verb are those forms that a student must memorize in order to be able to conjugate the verb through all its forms. The concept originates in the humanist Latin schools, where students learned verbs by chanting them in the four key forms from which all other forms can be deduced, for example: fero - ferre - tuli - latum ('to carry') Not all languages have to be taught in this way. In French, for example, regular verbs can be deduced from a single form, the infinitive, and irregular verbs are too random to be systematized under fixed parts. But the concept can be carried over to many languages in which the verbs have some kind of "regular irregularity", i.e. irregularity always occurs at the same place in an otherwise regular system. Although the term 'principal part' is usually applied to verbs, the same phenomenon can be found in some languages in nouns and other word types. It is normally restricted to regular verbs, nouns, etc., and applies to languages where the regular paradigm is based on more than one underlying form. It does not cover random irregularities. Classical languages Latin 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 the 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