51. A system for providing a natural language answer to a natural language question, the system comprising: an interface configured to receive, over a computer network, a query comprising a grammatical question; an interface configured to submit the query to a lookup engine; an interface configured to receive initial search results from the lookup engine, the initial search results comprising a plurality of documents, wherein the initial search results comprise a ranking of the plurality of documents according to relevance; a processor configured to identify, in the plurality of documents, a plurality of candidate sentences; a processor configured to calculate, for each candidate sentence, a measure of commonality between the candidate sentence and the query; a processor configured to assign, to each candidate sentence, a score, wherein the score comprises (1) a rank of the candidate sentence according to the ranking of the plurality of documents, and (2) the measure of commonality between the candidate sentence and the query; a processor configured to sort the candidate sentences according to score, whereby a rating of candidate sentences is produced; and an interface configured to send, over a computer network, a reply to the query, the reply comprising at least a top candidate sentence from the rating of candidate sentences.
51. A system for providing a natural language answer to a natural language question, the system comprising: an interface configured to receive, over a computer network, a query comprising a grammatical question; an interface configured to submit the query to a lookup engine; an interface configured to receive initial search results from the lookup engine, the initial search results comprising a plurality of documents, wherein the initial search results comprise a ranking of the plurality of documents according to relevance; a processor configured to identify, in the plurality of documents, a plurality of candidate sentences; a processor configured to calculate, for each candidate sentence, a measure of commonality between the candidate sentence and the query; a processor configured to assign, to each candidate sentence, a score, wherein the score comprises (1) a rank of the candidate sentence according to the ranking of the plurality of documents, and (2) the measure of commonality between the candidate sentence and the query; a processor configured to sort the candidate sentences according to score, whereby a rating of candidate sentences is produced; and an interface configured to send, over a computer network, a reply to the query, the reply comprising at least a top candidate sentence from the rating of candidate sentences. 58. The system of claim 51 , wherein each score comprises a geometric mean of (1) the rank of the candidate sentence according to the ranking of the plurality of documents, and (2) the measure of commonality between the candidate sentence and the query.