Mustalah Al-Hadith (Hadith Terminology) may be defined as a knowledge based on principles and maxims, by way of which one is familiar with the conditions of the chains of narrations and their texts, whether accepted or rejected.
According to the conditions of the chains of narration, the scholars of Islam have divided Ahaadith (plural of Hadith) into many categories.
For the sake of brevity, we will cover only some of these categories here, whilst in reality there are many more. The main 3 gradings Ahaadith fall into are:
It is the first category. It refers to the Hadith which can be said to authentically be traced back to the Messenger and is therefore accepted.
The conditions for a Saheeh Hadith are 5:
A Hasan Hadith is similar to a Saheeh Hadith, but one or more of its narrators have slightly less precision. They are still trustworthy, but their memory or accuracy is not as strong as required for a Saheeh Hadith. Because of this, the Hadith is ranked one level below Saheeh.
When there are many chains for the same Hadith, and each one is Hasan, their combined strength can raise the Hadith to the level of Saheeh li ghayrihi — meaning it is considered authentic because of the support from other chains.
In short, a Hasan Hadith is reliable, and if supported by many other chains, it can be treated like an authentic Hadith.
There are two types of Da'eef Ahadith, namely those with a light weakness and a severe weakness. If the former has multiple chains, they can be added up to reach the level of Hasan Li Ghayrihi, similar as is done with a Hasan Hadith to make it reach Saheeh Li Ghayrihi. This can only be done if the weakness is considered "light". As for the severe weakness, then this can never be made authentic.
The reasons for a Da'eef Hadith go back to deficiences in the conditions required for a Saheeh Hadith. Therefore a Hadith may be consideed weak for any of the below 4:
While we have introduced the basic types of Hadith according to their level of authenticity, this is only a small part of the broader science of Hadith classification. There are many more detailed discussions that scholars have explored — such as Hadith that are Mawquf (statements attributed to a companion), Munqati' (with a broken chain), or affected by Tadlis (a narrator hiding a defect in the chain). Hadith can also be classified based on who they are attributed to, the manner of transmission, or whether they are isolated or widely reported. The intent behind mentioning this here is to show that Hadith Sciences are an incredibly vast topic full to the brim with centuries of extensive scholarship, and no web-page of this sort would ever be able to do justice to the topic.
For the sake of brevity, we have not included all of these topics here. However, a page for further reading and structured study is available here.