Principle 2: Reading definitions does not prove that the makharij and inherent qualities have been mastered. Recite to a competent teacher, listen to the correction, and practice until the articulated sound is reliably accurate.
Principle 3: A deficiency in a quality may merely impair a letter's phonetic refinement, or it may be severe enough to distort or replace the letter's identity. These are not equal in effect or seriousness.
Example: replacing س with ص changes the consonant. Retaining the proper consonant but making its safir unbalanced is a different kind of deficiency. First determine whether the underlying letter has been preserved, then correct the relevant quality.