Simple transitions connect ordered landings (one foot at a time) to ordered takeoffs, in any order. There will be contact with both legs to the ground, but not in use simultaneously; momentum is gathered from a "push, jump" effect during takeoff from one leg to the other in sequence.
Common Simple Transitions
Vanish transition occurs each time the body weight is exchanged from the initial landing leg onto the other upon takeoff. During a Vanish, the landing order and the takeoff order will be the same (right foot, then left or vice versa) as if the landing had simply disappeared. An artificial form of Vanish called "Skip" is created whenever an adjustment is made to the position during the transition (this can be made Complex by using a jump to change position.)
The opposite Simple transition is called Reversal. This transition requires the reverse of the landing order for takeoff, meaning that the body weight is only temporarily shifted to the second leg, before being returned to the initial landing leg for takeoff into the second trick. Making a change in the position during a Reversal creates an artificial form called "Redirect" (one of the most common transitions in tricking.)