الْحُجَّةُ هِيَ الْمِيزَانُ فِي هَذَا الْبَحْثِ.
Evidence is the criterion in this inquiry.
The separation pronoun strengthens the predication and can, in suitable settings, support a reading of exclusivity. The claim presents evidence as the criterion for this inquiry, not a timeless denial of every other consideration.
In a debate against authority without evidence, the pronoun’s focusing role is particularly apt. Its mere presence does not establish that the audience was necessarily hostile.