Qere Perpetuum
In a few cases a change may be marked solely by the adjustment of the vowels written on the consonants, without any notes in the margin, if it is common enough that this will suffice for the reader to recognize it. This is known as a Qere perpetuum ("perpetual" Qere). It differs from an "ordinary qere" in that there is no note marker and no accompanying marginal note — these are certain commonly occurring cases of qere/ketiv in which the reader is expected to understand that a qere exists merely from seeing the vowel points of the qere in the consonantal letters of the ketiv.
For example, in the Pentateuch, the third-person singular feminine pronoun היא hī is usually spelled the same as the third-person singular masculine pronoun הוא hū. The Masoretes indicated this situation by adding a written diacritic symbol for the vowel to the pre-Masoretic consonantal spelling h-w-' הוא (see diagram). The resulting orthography would seem to indicate a pronunciation hiw, but this is meaningless in Biblical Hebrew, and a knowledgeable reader of the biblical text would know to read the feminine pronoun hī here.
Another example of an important qere perpetuum in the text of the Bible is the name of the God of Israel – יהוה (cf. Tetragrammaton). Often it is marked with the vowels יְהוָֹה, indicating that it is to be pronounced as אֲדֹנָי Adonai (meaning "my Lord") rather than with its own vowels. The consensus of mainstream scholarship is that "Yehowah" (or in Latin transcription "Jehovah") is a pseudo-Hebrew form which was mistakenly created when Medieval and/or Renaissance Christian scholars misunderstood this common qere perpetuum; the usual Jewish practice at the time of the Masoretes was to pronounce it as "Adonai," as is still the Jewish custom today. Pronouncing it as "Jehovah," "Yehowah" or similar would be a mistake of exactly the same type as reading hiw for the qere perpetuum of the third-person singular feminine pronoun.
Occasionally, the Tetragrammaton is marked יֱהוִֹה to indicate a qere of אֱלֹהִים Elohim, which itself is another Divine Name.
Read more about this topic: Qere, Types of Qere and Ketiv