Remember that the trust relationship in OpenPGP is not transitive. If you know that Alice&#x27;s key is valid and you trust Alice, then if Alice signs Bob&#x27;s key, you know that Bob&#x27;s key is valid. However, unless you also <i>personally</i> trust Bob, then you cannot trust any signatures that Bob makes. (Unless Alice&#x27;s signature also indicates trust in Bob; but this is not the common situation, think of e.g., keysigning parties.) Hence, if you have a path from you to Carol going through Alice and Bob, and you trust Alice but you do not know Bob, then you have no guarantees about the validity of Carol&#x27;s key (Bob may have signed a phoney key).<p>Of course, checking paths in the Web of Trust is not entirely useless, because a key which is connected to you probably has more chances to be valid. However, it offers no strong guarantee on trust unless you personally trust all intermediates along that chain.