Originally Posted by
Ruanark
No, I think you misread whatever said that. What happens is that BOTH SMN and SCH's lvls are dependent on your ACN lvl. So if you lvl ACN to 45 with SMN unlocked, SMN will be 45 when you equip the soul. If you swap to the SCH soul, the SCH will be lv45. Jobs do not have exp bars of their own, only the main class their tied too. (so SMN doesn't gain extra lvls from THM and SCH doesn't gain lvls from CNJ, only ACN for both)
Edit: To unlock SMN, you need THM at lv15. To unlock SCH, you need CNJ at 15. In addition, ACN must be 30+ and for each job, you have to do a quest to gain the Job Soul. After that, you can freely change jobs/classes between SMN/SCH/ACN by equipping/unequipping souls while on ACN.