1. A search method, said method comprising: accepting user input of a main query including a plurality of keywords; accepting user input that identifies at least one combination of said keywords inhibited to be used as a sub-query; generating a plurality of sub queries based on the user input each including one or more keywords by combining the keywords included in the input main query; excluding sub-queries that are identified as inhibited combinations; calculating a co-occurrence probability for the keywords of each sub-query; sorting keyword combinations in a descending order based on the co-occurrence probabilities; excluding from use as a sub-query any combination of keywords having a co-occurrence probability below a threshold; separately sending the generated sub queries to a number of search engines; re-searching a plurality of search results returned from the search engine in response to the plurality of sub queries, with the input main query; and displaying search results acquired by the re-searching step.