This post is a paraphrased (incomplete) translation, with my personal comments and notes, of the chapter pertaining to the rules of weakening or strengthening a narrator. This is from the book Buhuth fi ilm al-Rijal of Ayatullah Asif Muhsini. The Arabic for this can be found on page 18 of his book – he discusses 8 rules, but the following post only covers the first 2 rules. Once again, I have left many of the technical terms in their Arabic form and thus this post will only benefit those who have basic familiarity with the subject.
Regarding the Rules for Affirming or Weakening Someone
The lack or non-existence of hujjat for a narration that comes from a liar, and the non-existence of relying upon it or using it as a basis for anything, is from the axiomatic pieces of knowledge. Likewise, is a narration whose truth or falsehood is suspicious. Therefore, in order to determine the dependability of a narration, there is no choice but to struggle to determine its truth either through Ilm ul-Wijdani [intuitive cognition – which results in certainty], or through Ilm ul-Urfi [which results in Itminan].
Ilm ul-Urfi [or Itminan] is a hujjah as per the seerah of the uqalah, just like knowledge itself is hujjah for the intellect. Even though it is not explicitly mentioned in the Shari’ah, however we know that the Prophet and Imams acted upon Ilm ul-Urfi [i.e. they considered it hujjah], like the rest of the Uqala.
Itminan can be attributed to two things. Either to the notion that the narration was said by one of the Ma’sumeen [itmininan in its sudur], which can be reached through an internal or external qareenah (context) or, by determining the truthfulness of the reporter of a narration.
If the itminan regarding the truthfulness of a mukhbir, necessitates the truthfulness of a report [in its sudur] then there is no problem in relying upon it. However, if the itminan leads us solely to the truthfulness of a reporter, but does not lead us to itmninan regarding whether the report was indeed said by one of the Ma’sum, then there is debate over whether such a report has hujjiyah or not. The question that needs to be answered is if itminan of this type, is similar to a personal itminan which is hujjah and reliable.
From the two aforementioned options, the first option is closer to the truth. That is to say, solely looking at the truthfulness of a reporter should be enough to establish hujjiyah (unless of course there are other contextual factors that oppose it).
The truthfulness of a reporter can be established through determining their trustworthiness and their justice [adalah], or by seeing the proof of their goodness, or that they have been praised. The praise should signify the fact that the reporter was indeed truthful, and refute or diminish the possibility of him being a liar. Thus the praise should be a sufficient amount that proves such a thing, even if it doesn’t necessarily prove the piety of the reporter in other actions.
In regards to establishing the ‘adalah (justice), fisq (transgression), or just the truthfulness alone (even if he isn’t just in other actions), or the untruthfulness alone (even if he isn’t a transgressor in other actions), it is obligatory upon anyone who intends to study the condition of the narrators, to follow certain rules. If someone does not know these rules or is heedless of even one of the rules, he will not reach the truth, and there is no doubt in this.
Rule #1: Acquire the truthfulness of a reporter’s report regarding the trustworthiness or the truth of the narrators
This is because, there is no consideration given to a reporter who is a liar or his conditions are unknown, if he gives another person ta’deel (considers him ‘adil), or gives them jarh (invalidates their credibility). Due to this, for example, we do not take the words of individuals like Nasr bin Sabah (who has Rijali opinions in Rijal al-Kashi), or al-Uqayqi (someone who Allamah Hilli relies upon), and ibn Nadeem, because their trustworthiness is not established.
Likewise, we do not accept the testimony of a person about themselves, as it will necessitate circular reasoning. For example, if an unknown narrator narrates praise from an Imam regarding himself, we cannot determine his trustworthiness based on this. Rather, his trustworthiness needs to have been proven beforehand until we can accept such a narration from him about himself. How can we accept his words (if he is unknown), when it is nothing but a circular argument. Later, a detailed refutation will be presented against certain scholars of Rijal who suggest that the words of an unknown individual reporting a narration about himself should be accepted.
Rule #2: Unity in meaning of ‘adalah between one who gives someone ta’deel , with the one who intends to use a person’s ta’deel
Suppose that ‘adalah only meant accepting Islam – as it is attributed to Sheikh Tusi and Allamah Hilli, but for someone who wants to take their words, the meaning of ‘adalah for them means a disposition, the ta’deel of someone who holds the first meaning will have no benefit for the second person who holds a completely different meaning. This is an important point, and one must not be heedless of this.
However, in the chapter of Qadha in the book of Jawahir, the author says: What is known to be correct in the shariah’ is that a statement of a witness can be carried over if it correlates with reality, even if the witness did not mean it in the same.
I [Muhsini] say: We don’t believe in this principle as we have not found reliable evidence for carrying over the words of a witness (into a different scenario which he or she did not intend with their wordings). Thus we have no choice but to resort to al-Qaidah al-Awwaliyah [the first principle: if there is a different meaning of ‘adalah and a different understanding of it, don’t use the word and apply it on the meaning you intend]. This is in agreement with the view of Shaheed al-Thani in his Dirayah, and a detailed discussion regarding it will come in Chapter 30.
This rule provides great and important benefits, given that we understand tawtheeq as meaning ta’deel, like many of the mutakahireen have accepted, but if it just means tasdeeq, then it won’t have that many benefits.
Furthermore, I came across the words of Syed al-Khoei on this subject, and they are in agreement with what I have said [i.e the words should not be allowed to carry over] and they are against the words of Sahib al-Jawahir, and also against the view of Syed al-Hakeem.
 This is not referring to a hadith narrator, rather a person who gives the news of someone else’s trustworthiness
 For example, a person might say something, even though they intended to mean something else, but if the wordings correlate with reality and with what really happened, then those words can be used against him or for him