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When the runner finishes the race, the runner crosses the finish line. When the runner has finished the race, the runner is across the finish line.

In American football, the player scores a touchdown when any part of the ball breaks the (imaginary) plane of the goal-line (the plane is perpendicular to the playing surface). The player has scored a touchdown when that action is deemed to have taken place.

The difference is merely in how the event or action is understood. The facts "on the ground" are the same. We can understand the action as one in which a boundary is crossed or one in which a boundary has been crossed. It simply involves a shift of a virtual vantage point.

When the runner finishes the race, the runner crosses the finish line. When the runner has finished the race, the runner is across the finish line.

When the runner finishes the race, the runner crosses the finish line. When the runner has finished the race, the runner is across the finish line.

In American football, the player scores a touchdown when any part of the ball breaks the (imaginary) plane of the goal-line (the plane is perpendicular to the playing surface). The player has scored a touchdown when that action is deemed to have taken place.

The difference is merely in how the event or action is understood. The facts "on the ground" are the same. We can understand the action as one in which a boundary is crossed or one in which a boundary has been crossed. It simply involves a shift of a virtual vantage point.

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When the runner finishes the race, the runner crosses the finish line. When the runner has finished the race, the runner is across the finish line.