parsimony, principle of See OCKHAM’S RAZOR. parsing, the process of determining the syntactic structure of a sentence according to the rules of a given grammar. This is to be distinguished from the generally simpler task of recognition, which is merely the determination of whether or not a given string is well-formed (grammatical). In general, many different parsing strategies can be employed for grammars of a particular type, and a great deal of attention has been given to the relative efficiencies of these techniques. The most thoroughly studied cases center on the contextfree phrase structure grammars, which assign syntactic structures in the form of singly-rooted trees with a left-to-right ordering of ‘sister’ nodes. Parsing procedures can then be broadly classified according to the sequence of steps by which the parse tree is constructed: top-down versus bottom-up; depth-first versus breadthfirst; etc. In addition, there are various strategies for exploring alternatives (agendas, backtracking, parallel processing) and there are devices such as ‘charts’ that eliminate needless repetitions of previous steps. Efficient parsing is of course important when language, whether natural or artificial (e.g., a programming language), is being processed by computer. Human beings also parse rapidly and with apparently little effort when they comprehend sentences of a natural language. Although little is known about the details of this process, psycholinguists hope that study of mechanical parsing techniques might provide insights. See also GRAMMA. R.E.W.