in the verb paradigm. Even modern "irregular" verbs are not immune from analogy: For example, je vif, tu vis, il vit (vivre "to live") has yielded to modern je vis, tu vis, il vit, eliminating the unpredictable -f in the first-person singular. The simple past also shows extensive analogical reformation and simplification in Modern French, as compared with Old French. The Latin pluperfect was preserved in very early Old French as a past tense with a value similar to a preterite or imperfect. For example, the Sequence of Saint Eulalia (878 AD) has past-tense forms such as avret (< habuerat), voldret (< voluerat), alternating with past-tense forms from the Latin perfect (continued as the modern "simple past"). Old Occitan also preserved this tense, with a conditional value; Spanish still preserves this tense (the -ra imperfect subjunctive), as does Portuguese (in its original value as a pluperfect indicative). Verb alternations In Latin, stress was determined automatically by the number of syllables in a word and the weight (length) of the syllables. That resulted in certain automatic stress shifts between related forms in a paradigm, depending on the nature of the suffixes added. For example, in pensō "I think", the first syllable was stressed, but in pensāmus "we think", the second syllable was stressed. In many Romance languages, vowels diphthongized in stressed syllables under certain circumstances but not in unstressed syllables, resulting in alternations in verb paradigms: Spanish pienso "I think" vs. pensamos "we think" (pensar "to think"), or cuento "I tell" vs. contamos "we tell" (contar "to tell"). In the development of French, at least five vowels diphthongized in stressed, open syllables. Combined with other stress-dependent developments, that yielded 15 or so types of alternations in so-called strong verbs in Old French. For example, diphthongized to before nasal stops in stressed, open syllables but not in unstressed syllables, yielding aim "I love" ( amō) but amons "we love" ( amāmus). The different types are as follows: In Modern French, the verbs in the -er class have been systematically levelled. Generally, the "weak" (unstressed) form predominates, but there are some exceptions (such as modern aimer/nous aimons). The only remaining alternations are in verbs like acheter/j'achète and jeter/je jette, with unstressed alternating with stressed and in (largely-learned) verbs like adhérer/j'adhère, with unstressed alternating with stressed . Many of the non-er verbs have become obsolete, and many of the remaining verbs have been levelled;