How should word "C'tis" be pronounced?

[Agema]

There are hints looking at language development. For instance, "c" seems to have developed from "k" in much earlier Latin, which makes it very likely that it was pronounced hard, and there are other hints. You might be able to tell from poetry - inaccurate prounciation can wreck meter and rhyme.

Also I think that most of the population - even Italians in classical Rome - would not generally have spoken what we know as classical Latin, which was really a very formal and proper form used in literature and by the upper classes. Most people would have spoken Vulgar Latin, which would have varied greatly across nations and peoples in the Roman empire with some differences in pronunciation and vocabulary. You could compare with different uses of English worldwide, although the comparison fails at the level that English does not really have a formal standard in the way (to the best of my knowledge) that Latin did.

[Endoperez]

Originally Posted by Agema

English does not really have a formal standard in the way (to the best of my knowledge) that Latin did.

The formal standard of English is a very vulgar Latin. It's used in formal documents, encyclopedias, etc. The grammar has changed, but not the vocabulatory. Here's a short passage from Wikipedia article about Scientific Method, with non-Latin words emboldened and links to etymology for Greek and Latin words.

Scientific method refers to bodies of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. To be termed scientific, a method of inquiry must be based on gathering observable, empirical and measurable evidence subject to specific principles of reasoning.

[Agema]

Heh, nice one.

I might suggest the nearest that English has had to a formal language used in courts, literature and by the upper classes was around 11-14th centuries, and that formal language was French

Some Latin vocabulary was reintroduced via French, and more Latin and Greek was added because the people who used many terms of science and officialdom had extensive classical educations and made new words from them.