present modal view

Generally you use modal view controllers to focus the user's attention on a Task.  
 When you push, the user is in some kind of navigation flow, but still has the total application at their fingertips.   
 They might decide to go forward or backward, switch to a different tab in the middle, whatever.   
 When they get a modal view controller, they can't do any of that until the task is completed or canceled out of   
 (the modal view is dismissed).