Abstract: The present invention interprets natural language input using common sense reasoning. The invention avoids the combinatorial explosion that has occurred in other natural language understanding systems. The invention uses modules for parsing, disambiguation, formal semantics, anaphora resolution, and coherence, and a naive semantic lexicon. The naive semantic lexicon is consulted by the parsing, disambiguation, formal semantics, anaphora resolution, and coherence modules to determine whether an interpretation alternative is plausible based on the world knowledge contained in the naive semantic lexicon. The parsing module employs both a top-down and bottom-up parsing strategy. The parsing module consults the naive semantic lexicon to build a structure from natural language input that has both semantic and pragmatic plausibility. The invention uses a psychologically-motivated naive semantic ontology that provides a means for classifying concepts.