The categories that figure in Latin finite verb morphology are all displayed below, but this book is not meant to teach Latin. What we do mean to show is how the Romance languages reorganize the Latin system, retaining some categories with their original morphology, retaining others with new or recycled morphology, and creating new categories unprecedented in Latin.

Map of the Latin verb system

The Latin verb system, itself the product of drastic innovation on the way from Indo-European, took on a squarish architecture characterized by three binary contrasts: voice (active and passive), mood (indicative and subjunctive), and aspect (infectum and perfectum), in addition to the familiar category of tense (present, past, and future).Chart 7.1 shows the complete conjugation of cantāre ‘sing’ in the active voice. Its passive conjugation would occupy another chart of the same size (§ 7.9.4). This verb represents one of four conjugation classes. All four share identical endings in the perfectum.

From this display, what can we say about infectum forms and perfectum forms?

Every verb in Latin has one stem throughout the infectum and another throughout the perfectum. For cantāre ‘sing’, the perfectum stem is cantāv- [kantaw].

About perfectum stems

The infectum stem appears in the present infinitive. Given the infinitive, you may be able to predict the perfectum stem.