Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
Still more pedantic are the practices of making the fourth letter of quidquid a c to avoid the appearance of repeating a question, and of writing
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quotidie instead of colidie to show that it stands for quot diebus. But such practices have disappeared into the limbo of absurdities. It is often debated whether in our spelling of prepositions we should be guided by their sound when compounded, or separate. For instance when I say optinuit, logic demands that the second letter should be a b, while to the ear the sound is rather that of p: or again take the case of immunis: