Some people use accent marks in texts as if writing were a game of chance, avoiding the general rules of accentuation, disregarding the rules of diphthongs, hiatuses or monosyllables. These people tend to write in fits and starts, since they often have to stop writing and, in the best of cases, think about whether or not this or that word has an accent mark. Let's see as an example a term as frequent as day. Or is it spelled day? Day or day?
Someone may maintain that day should not have an accent because it is a monosyllable or acute word, but that is totally incorrect. In the first place, because it is a two-syllable word, that is, with two syllables (dí-a). Secondly, it is not acute, but flat: the accent, the greater intensity with which we pronounce the word, falls on the first syllable. However, in this case the rules of accentuation have little to do with it.
The confusion that the term generates in some people is due to the presence of two vowels in a row, with a stressed closed vowel (i) and another unstressed open vowel (a). Thus, a hiatus is produced that must always be marked, regardless of the accentuation rules for acute and flat words.
It should be remembered that when in a word there are two vowels in a row in the same syllable, a diphthong is formed, that is, it behaves like the same sound when pronounced. In cases such as "día" it is necessary to break the diphthong, creating two syllables -hiatus- and thus adjusting to the way in which we pronounce that word. And this is achieved by incorporating the tilde on the weak vowel.
Thus, the word day is always written with an accent, with the graphic sign on the letter i.
To avoid this type of doubt, there is nothing better than a brief review of the rules for accentuating diphthongs and hiatuses.
A previous question is to remember that the five Castilian vowels are divided into open and closed:
Having clear the division of vowels, we can say that a diphthong is the union of two different vowels that are pronounced within the same syllable: vien-to, sua-ve, viu-da, coin-ci-dir... As he points out the Pan-Hispanic Dictionary of Questions of the RAE, from the phonetic point of view the following vowel combinations can give rise to diphthongs:
Although, in speech, the sequence of two open vowels -especially when neither of them is tonic (petróleo, raedera)- can be articulated as a diphthong, this vowel combination is always considered hiatus from the normative point of view.
For its part, a hiatus is a sequence of two vowels that are pronounced in different syllables. There is a hiatus when one of these vowel combinations occurs:
According to the criteria of The Trust Project
