What is the difference between restriction (taqyīd) and specification (takhṣīṣ) in the Usul al-Fiqh?

To distinguish between takhsis (specification) and taqyid (restriction) in the principles of Islamic jurisprudence (Usul al-Fiqh), one must first understand the difference between amm (general) and mutlaq (unrestricted). Amm refers to a word that denotes all parts of the essence of its referent, such as "mankind" (al-insan) in the Almighty’s saying: "Indeed, mankind is in loss" (Quran 103:2). As for mutlaq, it refers to a word that denotes an essence devoid of any additional description, such as "a slave" (raqabah) in the Almighty’s saying: "then release of a slave" (Quran 4:92).

The difference between them is that the generality of amm is all-encompassing, covering all individuals, whereas the generality of mutlaq is substitutional, where a single individual suffices. Accordingly, takhsis (specification) applies to the amm, such as specifying "mankind" in Surat al-Asr with "Except for those who have believed" (Quran 103:3). And taqyid (restriction) applies to the mutlaq, such as restricting the prohibition of blood in the verse from Surat al-Ma'idah with "flowing blood" (daman masfūḥan) in the verse from Surat al-Anam (Quran 6:145).