Institutio Oratoria

Again what of those words which, although identical in the form of the nominative or present indicative, develop the utmost variety in their inflections. Thus from Alba we get both Albanus and Albensis, from volo both volui and volavi. Analogy itself admits that verbs whose present indicative ends in -o have a great variety of perfect formations, as for instance cado cecidi, spondeo spopondi, pingo pinxi, lego legi, pono posui, fiango fregi, laudo laudavi.

For analogy was not sent down from heaven at the creation of mankind to frame the rules of language, but was discovered after they began to speak and to note the terminations of words used in speech. It is therefore based not on reason but on example, nor is it a law of language, but rather a practice which is observed, being in fact the offspring of usage.