1. A method comprising the steps of: a) for each document in a plurality of documents, generating, by a computer system, text structure tags for the document, said text structure tags identifying a plurality of argumentative text types, wherein a text type comprises a type of argumentative content for an associated portion of a document, said types of argumentative content comprising an argument premise giving support, evidence, or reasoning for or against a conclusion or the conclusion comprising a resulting determination made using one or more argument premises; b) for each document in the plurality of documents, encoding, by the computer system, said document to generate a tree structure comprising a plurality of nodes, wherein said nodes correspond with said text types and hierarchical relationships among said nodes reflect argumentative relationships among said text types; c) selecting, by the computer system, a plurality of tree structures for the plurality of documents; d) combining, by the computer system, the plurality of tree structures as a single logical tree structure; and e) generating, by the computer system, a summary of the plurality of documents by: i) receiving from a user a selection of one or more particular text types for summarization; and ii) extracting, based on said text structure tags, portions of text from the plurality of documents that correspond to nodes from the plurality of tree structures to form a summary of the plurality of documents, the nodes corresponding to said one or more selected text types.