for an addition may either (1) involve no contradiction between it and the narration (2) of the one who did not include it; such an addition (3) is accepted outright, because it carries the ruling of an independent ḥadith (4) that a reliable narrator (5) transmits alone, with no one else relating it from his teacher.
Alternatively, (6) the addition may be contradictory, such that accepting it would necessitate rejecting the other report; in that case (7) preference is weighed between it and its opposing narration (8): (9) the stronger one is accepted and the weaker (10) set aside.
A number of scholars have become well known (11) for declaring that an addition is accepted in every circumstance, without distinction, (12) yet this cannot stand according to the methodology of the ḥadith critics, who stipulate that a ṣaḥīḥ report must not be shādh (anomalous) and who define shudhūdh as a trustworthy narrator contradicting someone who is even more trustworthy than he is.
What amazes one is that some of them have overlooked this point, even while acknowledging the requirement