1.  Class I. First and second conjugations. Changes e to ie, o to ue. These changes are due to stress of voice falling on the stem syllable. They occur in nine forms — the 1st, 2nd and 3rd persons singular and 3rd person plural of the present indicative and present subjunctive, and the imperative singular. Types: cerrar, 23,' contar, 24, perder, 25, and volver, 26. 340.

2.  Class II. Third conjugation. Changes

• to ie or i, o to ue or u. The changes, nine in number as in Class I, of e to ie and

• to ue, are due to stress of voice on the stem syllable. In addition, there are changes in twenty-three forms of e to i and of o to u. These are due to occurrence in the syllable following the stem, of a strong vowel that is stressed, either -a, -ió, or -ie-. These changes are found in the gerund, the 1st and 2nd persons plural of the present subjunctive, the 3rd person singular and plural of the preterite indicative, and the six forms of each of the following tenses: imperfect subjunctive, s and r forms, and the future subjunctive. See 541, 552. Types: sentir, 27, and dormir, 28. 341.

3. Class III. Third conjugation. Change, e to 1. These changes, which occur in

1 Light face numbers given after verbs refer to the section of the efpindice de verbos, pages 563 to 588, in which these verbs or their types are given.

ORTHOGRAPHICAL CHANGES   73

thirty-two forms, are due, nine of them, to stress of voice on the stem syllable, as in Classes I and II, and twenty-three of them to the fact that a strong stressed vowel occurs in the syllable following the stem. See 341. Type, pedir, 29. 342.

4.  There are a few verbs that vary in small details from the types given above. See in the Apendice errar, 23a, jugar, 24a, adquirir, 25a, oler, 26a, and reir, 29a. Errar

•  yerro, etc.; no word may begin with a diphthong, hence ye- instead of ie-. Jugar

•  juego ; this verb is an exception, the u becoming ue when stressed. Adquirir — adquiero, etc.; this verb is also an exception, the i changing to ie when stressed. Oler — huelo, etc.; since no word may begin with a diphthong, h is written before ue. Reir —rio, etc.; the weak vowel i must bear a written accent in all the singular and the third person plural of the present indicative and of the present subjunctive in order to retain the stress on the stem: rio, ria, etc.; and in the preterite and the tenses derived therefrom: rio, rieron, riese, etc., contractions for riio, riieron, riiese, etc. Compare pedir, 29. 343.

5. Orthographical-changing verbs. The consontal sound in which the stem terminates must be preserved. The spelling is changed