Confused

Last weeks class was very interesting. I must ask a question though. I am still very confused about the difference of a patent and a clause in the patent.

I understand that a clause is something in a patent. However,  I still don't understand whether one can sue over a patent protection void, or instead a clause problem. 

In last weeks lecture the interim professor did not give a clear answer. While I learned a lot and most of his lecture was fantastic, this question was not clearly and directly addressed. Do any of you understand? A few of you raised questions about this last week, so let me know. When you sue someone for patent infringement, do u sue about the entire patent or just the clause???

 Let me know below!! Thanks!