Ilmu ini adalah ilmu tentang kaidah-kaidah yang dengannya diketahui keadaan sanad dan matan hadis. Tujuannya adalah untuk membedakan hadis sahih dari yang lainnya. Ilmu ini terbagi dua: ilmu hadis riwayat dan ilmu hadis dirayat. Ilmu hadis riwayat mencakup periwayatan ucapan Nabi ﷺ, perbuatan, persetujuan, dan sifat-sifat beliau ﷺ, dari segi cara meriwayatkannya, ketepatannya, dan penulisan lafaznya (tahrir alfaz). Adapun ilmu hadis dirayat, melaluinya diketahui hakikat, syarat, jenis, dan kaidah periwayatan, serta keadaan para perawi, syarat-syarat mereka, jenis-jenis periwayatan, dan hal-hal yang terkait dengannya. Dirayat juga mencakup pengetahuan tentang makna yang terkandung dalam hadis, yaitu apakah ia bertentangan dengan nas yang qath'i.

It is the science of those laws whereby the condition of the sanad [chain of transmission] and matn [text of the ḥadīth] is known. Its objective is to differentiate the sahīh hadīth from the others. It is of two types: the science of hadīth pertaining to transmission [riwāya] and the science of the hadīth pertaining to meaning [dirāya]. As for the one pertaining to transmission, it includes the transmission of the sayings of the Prophet , his actions, consent and attributes, with repsect to their narration, accuracy and transcription of words [tahrīr alfādh]. As for the one pertaining to the meaning, the reality, conditions, types and rules of transmission are known through it, as well as the state of the transmitters, their conditions, the types of the transmissions and that which is related to it. Dirāya also covers knowledge of the meaning contained in the hadīth in terms of whether it contradicts a definitive text.