When nothing does something: The proliferation and triumph of the third person plural preterite variant ending -eron in Old and Early Modern Spanish

Abstract It is well known that the Spanish third person plural of -er and -ir verbs has two different preterite endings: primary -ieron, and the variant -eron, which appears after stem-final -j, e.g., dijeron, trajeron, tradujeron, etc., and that -eron arose from -ieron through absorption of the semiconsonant [j] into the Old Spanish stem-final palatal -x [ʃ], e.g., dixieron > dixeron. What is not so well known is that OSp. dixiemos, dixiestes, like dixieron > dixeron, likewise reduced to dixemos, dixestes, but unlike dixeron, did not survive. It is also to date unknown that the reduction of -ieron > -eron occurred in other grammatical categories, e.g., OSp. cogieron > cogeron, before reverting to -ieron. The present study will show when -eron first arose and became the predominant variant of the two after -x, the extent to which it arose in other grammatical categories, and will explain why vertical vocalic symmetry between OSp. dixiemos, dixiestes, dixieron, later dixemos, dixestes, dixeron, was ulimately broken, and how the loss of dixiemos/dixemos, dixiestes/dixestes on the one hand, and the triumph of dixeron on the other, are completely interconnected, ironically tied to the same historical linguistic phenomenon, and actually two sides of the same coin.