well you won't be able to define the starts and ends at the same time as you create your cost distance origins, since they will just loop back on to themselves. When you run the cost distance, they are from an origin point or points and radiate outwards. When you run the cost path, you start at the destinations and find the shortest path back to the origins... so if you have the origins and destinations at the same location, then it will go nowhere. For instance, a Path distance between two separate points on two separate ponds, might allow you to examine the directional differences between them. In a simple cost distance, it is highly likely the path from A to B is the same as B to A, however in path distance analysis, you can factor in directional costs, potentially resulting in different paths between the point pairs.
