1. A computer-implemented method for selecting an answer to a factual query, comprising: receiving a factual query; searching a fact repository to identify a set of possible factual answers to the factual query, wherein the fact repository stores factual information extracted from a plurality of documents; determining respective scores for at least a subset of the possible factual answers; identifying a first answer of the subset of the set of possible factual answers to the factual query, the first answer having a best score; identifying, as an answer that is contradictory to the first answer, a second answer of the subset, wherein the second answer is the best scoring answer that is contradictory to the first answer; and generating a response including the first answer only if the score of the first answer exceeds a predefined threshold and exceeds the score of the second answer by at least a first predefined margin.