or u, respectively, and the digraph ou was differentiated from o, even though many speakers now pronounced both as . These distinctions have close parallels in the orthographies of other West European languages. Since word stress can be distinctive in Portuguese, the acute accent was used to mark the stressed vowel whenever it was not in the usual position, more or less as in the orthographies of Spanish and Catalan. For example, the verb critica "he criticizes" bears no accent mark, because it is stressed on the syllable before the last one, like most words that end in -a, but the noun crítica "criticism" requires an accent mark, since it is a proparoxytone. Since the height of the vowels a, e and o is also distinctive in stressed syllables (see Portuguese phonology), high stressed vowels were marked with a circumflex accent, â, ê, ô, to be differentiated from the low stressed vowels, written á, é, ó. The choice of the acute for low vowels and the circumflex for high vowels went against the conventions of other Romance languages such as French or Italian, but it was already commonplace in Portuguese before the 20th century. (In many words, Portuguese ê and ô correspond to the Latin long vowels ē, ō.) Nasal vowels and nasal diphthongs usually appear before the orthographic nasal consonants n, m, in which case they do not need to be identified with diacritics, but the tilde was placed on nasal a and nasal o when they occurred before another letter, or at the end of a word. Although the vowel u can also be nasal before other vowels, this happens in so few words (mui, muito, muita, muitos, muitas) that marking its nasality was not considered necessary. The acute accent was used also to mark the second vowel of a hiatus in a stressed syllable, where a diphthong would normally be expected, distinguishing for example conclui "he concludes" from concluí "I concluded", saia "that he leave" from saía "he used to leave", or fluido "fluid" from fluído "flowed". Initially, the orthographic system, both in Brazil and Portugal, determined the usage of diacritics in cases where two words would otherwise be homographic but not homophonous, such as acôrdo, "agreement", distinguishing it from acórdo, "I wake up". This principle was abandoned in all but a dozen cases in 1945 in Portugal and in 1973 in Brazil. (In most cases the