1. In a speech recognition system, means for dynamically adding words to an existing recognition vocabulary defined by a lexical network, said means comprising: A. means defining a plurality of phonetic constraint nodes characterized by phonetic constraint tuples (s, y, z,... ) of order two or greater, where x, y, z,... are constraints on the word to be added to the vocabulary; B. means defining a plurality of word class nodes, each characterized by a word class and a phonetic constraint; C. means defining a plurality of connection nodes, each characterized by a phonetic constraint; D. means for establishing links between said word class nodes and said phonetic constraint nodes, and between said phonetic constraint nodes and said connection nodes, for a base vocabulary, prior to the time of dynamic word addition to said lexical network, in accordance with a predefined congruence between the phonetic constraints of said word class nodes, said phonetic constraint nodes and said connection nodes; and E. means for adding to said network words defined by at least beginning and ending phoneme nodes and characterized by at least one phonetic constraint, said means comprising means for establishing links between said beginning and ending phoneme nodes and said word class nodes in accordance with a predefined congruence between the phonetic constraints of said words and those of said word class nodes.