I would like to ask about a pronunciation rule that looks universal. There are (at least) 1201 words in English ending with "ous" and the majority of them are adjectives (http://www.morewords.com/ends-with/ous/). A random check shows that adjectives ending with "ous" are pronounced with "əs" at the end.
There are as well at least 68 words ending with "cious", like conscious, and apparently they are pronounced with "ʃəs" at the end (ˈkɒnʃəs).
Question. Do these two rules hold universally for adjectives? If yes then how such rules can be explained? (we know all that in English there are few pronunciation rules). Are there further rules of a similar nature?