The letters of the alphabet divide into two categories: original (asliyyah) and secondary (fari'ah)¹.
The originals: twenty-nine letters according to the most widespread view, the first being the alif and the last the ya'.
The secondaries: they are those that come out from two makharij, or that hesitate between two letters or two sifat. They are eight in number:
The hamzah mushkilah (between two): the one that is pronounced between the hamzah and the alif, as in أَأَعْجَمِيٌّ ², or between the hamzah and the ya', as in أءِنك ³, or between the hamzah and the waw, as in أءُنْزِل ⁴, among the reciters other than Hafs for these two last examples.
The mumalah alif (inclined): the one that is pronounced inclined toward the ya'. It is specific to Hafs in the word مَجْرَاهَا ⁵ of Surah Hud.
The sad mashma' (blended) with the sound of the za': as in الصِّرَاط ⁶ in the recitation of Hamza, where it is pronounced blended with the sound of the za'.
The ya' mashma' with the sound of the waw: as in قِيلَ ⁷ in the recitation of al-Kisa'i and of Hisham, where it is pronounced blended with the sound of the waw.
The mushabba' alif (emphasized): when the alif follows an emphasized letter (mufakhkhamah), it follows it in emphasis, whereas its original state is thinning (tarqeeq), as in الطَّامَّة ⁸.
The mushabba' lam: in the name of Majesty (Allah) when it is preceded by a dammah or a fathah, as in عَبْدُ اللَّه ¹, قَالَ اللَّهُ ², knowing that the original state of the lam is thinning³.
The mukhaffayah noon (concealed): when it blends with the letter that follows it, as in يَنكُثُونَ ⁴.
The mukhaffayah meem: it is like the noon; both, when concealed (ikhfa), become two incomplete letters (naqisah), as in أَنْبِئْهُمْ بِأَسْمَائِهِمْ ⁵.
Additional examples (Qawa'id al-Tajwid on the recitation of Hafs)