What is Isnad and Matn in islamic literature

Isnad: The Sanad (chain) of narrators was carefully studied. Each and every narrator was observed closely and his character investigated into. His faith, memory, knowledge of the Quran and Arabic language, and character had to be of the highest degree for the Muhaddith to accept his statement.

Moreover, the chain was required to be complete and uninterrupted. Each narrator was required to be known to the preceding and the succeeding narrator. Otherwise, the chain would be disapproved, and also the Hadith would be barred from being authentic. For this purpose, another branch of Islamic science was developed, known as Asma al Rijal, (the science of men) which comprised detailed investigations of the biographies of the narrators.

Matn: The text of the Hadith is called the Matn. It must be examined carefully. Each and every word must be scrutinized. The actual text of the Hadith has to conform to the Holy Quran and the already verified Ahadith. Also, it must be in the style and manner of the Holy Prophet (ﷺ), as well as the literary style of the Arabs of that time.

This refers to the tongue spoken by the Messenger of Allah. It should not have any modern words that didn't exist at the time of the Messenger of Allah. There shouldn't be any vulgar or odd language that the Messenger of Allah cannot be expected to use. It should not differ from established laws of nature. If it clashed with any of these, it couldn't be included in any authentic book.