Forming Infinitives
These rules apply to most verbs. Some verbs are irregular, and their infinitives must be memorized.

• The Present Active Infinitive is one of the four priniciple parts of a verb, and must generally be memorized. Eg., amare, habere, ducere, capere, audire
• To form the Present Passive Infinitive of -a, -o and -i declension verbs, drop the -e from the end of the present active infinitive and add -i. For -e/-i declension verbs, drop -ere and add -i. Eg. amari, haberi, duci, capi, audiri
• The Perfect Active Infinitive is formed by adding the ending -sse to the third principal part. Eg. amavisse, habuisse, duxisse, cepisse, audivisse
• The Perfect Passive Infinitive is simply the fourth priniciple part (the perfect passive participle) and "esse," the infinitive of "sum." Eg. amatus esse, habitus esse, ductus esse, captus esse, auditus esse
• The Future Active Infinitive is formed by adding -ur- to the fourth principal part before -us, -a, -um, pluse "esse." Eg. amaturus esse, habiturus esse, ducturus esse, capturus esse, auditurus esse
• The Future Passive Infinitive, also called the Supine, is rarely used in Latin. It is formed from the neuter nominative singular form of the fourth principle part and "iri," the present passive infinitive of "eo." Eg. amatum iri, habitum iri, ductum iri, captum iri, auditum iri