This category of mistakes differs from the first in terms of severity.

These are termed “subtle” or “imperceptible” errors, as they do not directly contradict the rules of the Arabic language, nor do they alter the meaning of the Quranic text. However, they do become apparent when they conflict with specific Tajweed rules.

Referred to as “الخفِي – al-khafiy,” these errors are typically discernible only to those well-versed in Tajweed.

Instances of al lahn al-khafiy arise when certain recitation rules are disregarded. These may include neglecting the rules of madd (prolongation), failing to observe a rule of ikhfâ (concealment), or not producing the ghunna (nasal sound) when required.

Scholars in the field of Tajweed generally consider lahn al-khafiy to be “makruh” (disliked), though there is some variation of opinion. Some scholars also classify these errors as “haram” (forbidden), but to a lesser degree than the more serious mistakes.

For example, pronouncing أُنْزِلَ without applying the ikhfa rule over the letter ن by pronouncing it as a single ن doesn’t change the word’s meaning. Still, it represents a breach of the established recitation rules that should be corrected.