Private is a different concept from Known. Known is related to Idea. 
Voice is related to Mechanism. Control is a type of Mechanism. Control is related to Tower. Tower is related to Height. 
Private <--DistinctFrom--> Known <--RelatedTo--> Idea 
Voice <--RelatedTo--> Mechanism <--IsA-- Control <--RelatedTo--> Tower <--RelatedTo--> Height 