Can I include in my CV the invitation to a conference I'm not sure to attend? I have seen this question (Unable-to-attend conferences in CV), but the situation is a bit different. In my field, we don't usually submit papers for conferences. Rather, the organizers directly invite a number of persons whom they think interesting to give talks (sometimes participants can contribute talks or posters, but that is not the case here). I received such an invitation, but for a number of reasons am not sure yet whether I will attend. 

Can I still add the invitation to my CV?

One could of course argue that it is strange to get credit for something (a talk) I might not do. But one could also think that the invitation itself is a distinction and therefore worth mentioning.
I would say no.

I often turn down invitations that could be considered a distinction, i.e. an indication that somebody thinks I am reasonably competent at this research thing:


Will you speak on this panel at this research open house?
Are you willing to review this paper for this journal?
Would you want to do a research internship with us this summer?
Do you want to submit an invited paper to this workshop?
Can you mentor this undergrad who is doing research in the lab?


All of these things would go on my CV if I actually do them, but not if I turn down the invitation.

An invitation to speak at a conference is no different, in my opinion. It's certainly a nice validation of your work that the conference organizers recognized your ability to contribute. But if you don't actually give the talk, it doesn't go on the CV.