Word endings which sound like 'shul' are spelt -cial or -tial
-cial is commonly used after a vowel - e.g. spe cial or offi cial
-tial is commonly used after a consonant - e.g. par tial or poten tial
As always, there are certain words which don't follow the rule! Examples are initial, financial, commercial and provincial.
Word endings which sound like 'shous' are spelt -cious or -tious
If the root word ends in -ce the sound is usually spelt as c - e.g. grace - gracious or malice - malicious.
Example words are - vicious, precious, delicious, suspicious and ambitious, cautious infectious.
As always, there are certain words which do not follow the rule - for example, anxious.