How to spell the 'shun' sound

The 'shun' sound can be spelt in three different ways. Which one you use depends on the last letter or letters of the root word.

If the root word ends with 'c' or 'cs' use the -cian suffix: magic - magician
When the root word ends with 'd' or 'se' the suffix used is usually -sion: expand - expansion
If the root word ends with 't' or 'te' use -tion: invent - invention