Institutio Oratoria

Again the following distinction has frequently been observed: ad is spelt with a d when it is a preposition, but with a t when it is a conjunction, while cum is spelt quum when it denotes time, but cum when it denotes accompaniment.

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

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:

the letter n, which is required by strict adherence to fact, is forced by the sound of the m. which follows to change into another m.

We must also note when analysing compound words, whether the middle consonant adheres to the preceding syllable or to that which follows. For example since the latter part of haruspex is from spectare, the s must be assigned to the third syllable. In abstemius on the other hand it will go with the first syllable since the word is derived from abstinentia temeti,

abstention from wine.