WHICH WORD?

to think about to think of

This is difficult to explain and more difficult to understand and use correctly.  

​The short explantion is below.
to think about + verb + in

​doing something - action, opinion

​This is used the most.

  1. What are you thinking about?
    Sales!  They are way down.

  2. I hate my job.  I'm thinking about joining the Army.

  3. He has been thinking about getting a job with Google in Mountain View; their HQ.

  4. If you are thinking about leaving medical school, I'd think twice.
to think of + noun, noun phrase

​someone or a situation - considering, feeling
​Used less than "to think about"

  1. What do you think of my new hairdo?

  2. I was thinking of my Mother.  She died a year ago today.​

  3. You look sad.
    Yeah, I was thinking of all the poor kids in Syria. 

  4. Have you been thinking of me?
    Sure.  Every day.