Shulchan Aruch is the default view only when Achronim are deadlocked

from Daas Torah - translation is copyrighted

Chazon Ish (C.M. 1:1 Likutim): Concerning the matter of the dispute over semicha in post-Talmudic times, the deciding factor in halachic matters is always according to which side has proofs which are stronger and more reasonable. Even though we normally follow the Shulchan Aruch – nevertheless were are accustomed to deviate from the Shulchan Aruch because the Achronim deviate from its rulings with correct proofs according to the understanding of the gedolim in each generation. So therefore for each halacha we are forced to study the analysis of the Achronim because intellectual reasoning is the decisive factor. However when the matter is deadlocked because the sides are equal – then we follow the disputant who is greater and that is why we accept the rulings of the Beis Yosef and Rema. So therefore in the dispute concerning semicha – according to our understanding those who rejected the new semicha are more cogent and understandable. Those who supported it are not understandable.