Effective communication means the transference and understanding of meaning. but you cannot know if someone has received your message and comprehended it in the way that you meant unless you seek:

I believe the answer is: Feedback

When you receiving feedback from your communication partner, you can analyze whether he/she has the full scope of the communication content by judging from their expression and word choices.
Without this, it is very hard to gauge whether both of you are in the same page or not.