Confusion de ja vu in Section 31 of CPC - Limitation Period for Recovery of Money Due

Maine 5 times padhai ki hai, phir bhi ye Section X ka kuch samajh nahin aaya. Koi log bata sakte hain ki jo kuch maine seekha hai, wahi galat hai ya phir koi dusri galti? Maine padha hai ki Section 31 ke hisab se, if someone files a suit for recovery of money due within 3 years from date of cause of action, it's all good, right? But then phir Section 31 (4) ke hisab se, if the plaintiff has a knowledge of cause of action within 3 years, the limitation period starts from that day. Kya ye don't contradict the first part?