Common-neighbour counts provide a basic path-based score for a possible missing link.

If two unconnected nodes share many neighbours, the graph supplies a local reason to suspect an absent edge: the candidate would close several two-step paths or triangles. More refined scores include Adamic–Adar, which discounts common high-degree neighbours, and Katz, which sums paths while penalising longer ones. These heuristics are not proofs. They encode a structural hypothesis: local proximity, especially through informative intermediaries, makes a connection more plausible.