A natural language understanding system may be given the capability to construct a semantically detailed parse tree for each acceptable interpretation of an input natural language expression (or fewer such parse trees than interpretations) by independently solving sub-trees corresponding to various series of post nominal modifiers and associating those partial solutions with corresponding nodes in the overall parse tree. The argument order in predicate calculus atomic formulas may be standardized in a manner that supports the use of a chart parser applied to a head-driven phase structure grammar and that permits a simplified more tractable grammar that in turn can be used as a domain general semantic grammar.