呼就係合口、開口，大體上等同於介音嘅有無，但係又毋係都係咁。韻圖中不合此例嘅「開、合」劃分，有一些，學者認為係傳抄刊印嘅錯誤。另一些則主要涉及到古人對脣音字，和合口韻尾等音嘅語感。古人有將脣音字同埋合口韻腹、韻尾睇成係合口呼嘅傾向，而無論呢啲字是否帶介音——好似《韻鏡》「外轉第二十六」所列的霄、小、笑韻就被界定爲「合口呼」。開口、合口與介音嘅有無也往往是學術上爭論的焦點。
Exhalation is the closing of the mouth and the opening of the mouth, which is roughly equivalent to the presence or absence of the intermediate, but it is not necessarily the same. Some of the inconsistencies in the rhyme diagram are considered by scholars to be errors in copying and printing. Others mainly involve the ancients' sense of language for labial words, common oral rhyme endings, etc. The ancients had a tendency to regard labial words and chorus rhyme and rhyme as the final conjunction, and whether or not the word has a mesophon or not, such as the xiao, xiao, and laughing rhymes listed in the "Outer Turning 26" of the "Rhyme Mirror", were defined as "hekou hu". The presence or absence of openings, closings, and intersonants is also often the focus of academic debate.