Dynamic and stative

Some verbs can be both action verbs and dynamic verbs depending on their meaning:

1. Be

• be = it is usually used as a stative verb - stative
  He's an excellent guitarist.

• be = when it means behave or act, it can be used as a an action verb in the continuous form. - dynamic
  You are being silly.
  

2. Think

• think = to express an opinion, to believe - stative
  I think it's a fantastic idea.

• think = consider, to reason about or reflect on, ponder, to have or formulate in the mind - dynamic
  I am thinking about my friend

3. Have

• have = to possess, to own - stative
  He has a beautiful car

• have = when it doesn't mean own or possess - dynamic
  He's having lunch.

4. See

• see = to perceive with the eye, to understand - stative
  I see what you mean.

• see = to meet, to be in the company of, to escort, to attend - dynamic
  He's been seeing the same woman for eight years.

上面think作为静态词时，的举例"I think it's a fantastic idea."  这里的think是谓语

而think作为动态词的例子,"I am thinking about my friend" 是be+doing的形式

像be作动态词，此时举例是are being, 

have作动态词，是is having 

这是为什么呢？为什么静态词作谓语时 不需要像 动态词一样是be doing形式  多了一个be动词还是ing形式？