1. A method of determining a combination of terms that represents subject matter of a natural language sentence, the method comprising the steps of: a computer determining respective numbers of words from a beginning of the sentence to respective terms in the sentence that match terms in the combination of terms; the computer dividing the sentence in a multiplicity of natural language phrases including a complex phrase and first and second simple phrases extracted from the complex phrase, the complex phrase being less than an entirety of the sentence; based in part on (a) the respective numbers of words from the beginning of the sentence to respective terms in the sentence that match terms in the combination of terms, (b) whether all terms of the combination are contained in the first and/or second simple phrases, and (c) whether all terms of the combination are contained in the complex phrase but not contained in the first and/or second simple phrases, the computer determining a confidence level indicating how well the combination of terms represents a condition or problem which is the subject matter of the sentence; the computer generating a table having a top row and other rows, the top row including entries that include respective words in the sentence that match terms in the combination, the other rows including entries that include the multiplicity of natural language phrases, the other rows including first and second rows, the first row including the first and second simple phrases, and the second row including the complex phrase; the computer determining respective numbers of rows from the words in the top row that match the terms in the combination to the first row if all terms in the combination are contained in the first and/or second simple phrases, or to the second row if all terms in the combination are contained in the complex phrase but not contained in the first and/or second simple phrases, wherein the step of determining the confidence level indicating how well the combination of terms represents the condition or problem which is the subject matter of the sentence is further based in part on the numbers of rows from the words in the top row to the first or second row; the computer determining that the confidence level exceeds a threshold; in response to the step of determining that the confidence level exceeds the threshold, the computer retrieving contextual information from a knowledge base, the contextual information being related to the subject matter of the sentence; and based on the confidence level exceeding the threshold, the computer determining that the contextual information retrieved from the knowledge base is a cause of the condition or problem which is the subject matter of the sentence.
2. The method of claim 1 , further comprising the step of: the computer determining whether a negation is included in a phrase in the sentence, the phrase including a term included in the terms of the sentence that match the terms in the combination of terms, wherein the step of determining the confidence level indicating how well the combination of terms represents the condition or problem which is the subject matter of the sentence is based in part on the negation being included in the phrase in the sentence.