How do you do four?
Well, two in one hand, and two in the other. 
You can use the same methods as mentioned earlier; columns, round-n-round (one way, or the other),
and forks. Additionally, since you are using two hands, you can either move your hands in
the same direction at the same time (synchronous) or you can move them in the opposite
directions (asynchronous or alternating). In other words, when the left hand goes up the
right hand is going down. The synchronous method has both hands going in the same
direction at the same time. Typically, when juggling even numbers of objects the
items do not cross over or switch hands. That said, I now give you a violation of that
situation...
Another method to do four is by tossing two across at the same time (one slightly below
the other), and whilst they are coming down throw the other two across. This method does
work, but you run the risk of having your balls collide if you do not carefully adjust the
tosses so there is a major and minor arc each time.
