effective----有效果的：The medicine is quite effective,for I am much better now.
effectual----能达到想要的结果：Tutoring is an effecual remedy to those who are slow in the classroom learning.
或者
perceptual----有关认知的：perceptual skills / problems
perceptive----理解力强的,有洞察能力的 a perceptive commernt / It was very perceptiveof you to notice the weakness in our plan.那以 -ual 结尾的 和 以-tive 结尾的 有没有通式来解释？便于理解你好。没有，英语的构词法是所有字母语言中最没有规律的。You have to memorise them one by one..