Allen and Greenough's New Latin Grammar, section 21

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INFLECTION.

21.

Latin is an inflected language.

Inflection is a change made in the form of a word to show its grammatical relations.

a. Inflectional changes sometimes take place in the body of a word, or at the beginning, but oftener in its termination: -

vox, a voice; vocis, of a voice; voco, I call; vocat, he calls; vocet, let him call; vocavit, he has called; tangit, he touches; tetigit, he touched.

b. Terminations of inflection had originally independent meanings which are now obscured. They correspond nearly to the use of prepositions, auxiliaries, and personal pronouns in English.

Thus, in vocat, the termination is equivalent to he or she; in vocis, to the preposition of; and in vocet the change of vowel signifies a change of mood.

c. Inflectional changes in the body of a verb usually denote relations of tense or mood, and often correspond to the use of auxiliary verbs in English: -

frangit, he breaks or is breaking; fregit, he broke or has broken; mordet, he bites; momordit, he bit.[1][The only proper inflections of verbs are those of the personal endings, and the changes here referred to are strictly changes of stem, but have become a part of the system of inflections.]