Consider the first diagram, Black has an eye () in the corner. To capture the Black stones, White must play on last, and must play on all the points , and , before that. The points are direct liberties, while the points are approach-move liberties, which must be played before the matched -liberties.

In the second diagram, White still has to play all the -points. However, now White does not need to play the last (potential) approach-move liberty . Obviously, White still has to play the other two -points. From this diagram, we can see that, if we have just one / pair, then they are equivalent to only one real liberty. We can also see that, for every other / pair that we add, we get two more real liberties - both the , and the , have to be played.

By comparing both diagrams, we can see that the addition of an eye, not only adds a liberty in the eye itself (), but also promotes the (last) potential approach-move liberty (a ) into a real one (an ), thus gaining a real (approach-move) liberty for Black.