What is the difference between 绝对 and 肯定? Continuing from my previous question, there's another phrase that also makes me confused, the usage of "绝对" and "肯定".

From my textbook, here's the meaning of each word:


  
  绝对 = [Adj./Adv.] Absolute / Absolutely.
  肯定 = [Adj./Adv.] Sure / Surely.
  


I'm assuming the level of confidence is different based on the meaning. The degree of "绝对" seems higher than "肯定".

Take a look at these sentences (taken from 汉语口语速成: 基础篇 pp. 91-92):


  
  老王点点头，给了老董一个肯定的回答。
  这个人这么胖，绝对不是张英。
  事情都有好的方面，也有不好的方面，不能想得太绝对。
  河里的水真清，要是不去游游泳，肯定很舒服。
  


Are the above sentences correct? Can "绝对" and "肯定" be used interchangeably? I feel sentences #1, #2, and #4 can be changed into "绝对", "肯定", and "绝对" respectively.
The dictionary definition may help you.

肯定 / kěn dìng /
1 （承认事物的存在或真实性） affirm; approve; confirm; regard as positive:
affirm the achievements
肯定成绩
2 （正面的） affirmative:
Her answer is in the affirmative.
她的回答是肯定的。
3 （明确的; 确定的） definite; positive; sure:
We are not sure yet whether we'll go or not.
去不去， 我们还不能肯定。
It's definite that he'll come.; He is sure to come.
他肯定会来。
4 （一定; 无疑问） certainly; surely; definitely; undoubtedly; as sure as eggs
is eggs; dead cert:
We can certainly have the job finished on time.
我们肯定能按时完成任务
绝对 / jué duì /
1 （没有任何条件; 不受任何限制） absolute:
absolute predominance; overwhelming superiority; absolute superiority;
绝对优势
oppose absolute equalitarianism;
反对绝对平均主义
2 （完全; 一定） absolutely; perfectly; definitely:
absolutely reliable;
绝对可靠
Absolute perfection in a dictionary is rare.
绝对完美的词典是罕见的。

Back to your examples:


老王点点头，给了老董一个肯定的回答。// 绝对 can not be used to replace 肯定

这个人这么胖，绝对不是张英。// 绝对 can be used to replace 肯定

事情都有好的方面，也有不好的方面，不能想得太绝对。//  绝对 can not be used to replace 肯定

河里的水真清，要是不去游游泳，肯定很舒服。//  肯定 can be used to replace 绝对.