Without the use of ordered rules, Uruguayan Spanish could be interpreted as having two additional phonemes and morphophonemic vowel alternation with its plural marker. Attempting to construct a diasystem that encodes such a variety would thus represent all Spanish varieties as having seven vowel phonemes (with contrasts only in final position). Due to both varieties having closed allophones of mid vowels in open syllables and open allophones in closed syllables, using ordered rules minimizes the differences so that the underlying form for both varieties is the same and Uruguayan Spanish simply has a subsequent rule that deletes at the end of a syllable; constructing a diaphonemic system thus becomes a relatively straightforward process. suggests that the rules needed to account for dialectal differences, even if not psychologically real, may be "historically" accurate.