As long as the holder of the Blades of Reason is alive at the end of the battle, the Dark Angels player rolls a D6 for each enemy model that was slain; on a roll of a 6, they do not die and are instead captured by the Dark Angels. Each captured prisoner adds +D6 victory points to the Dark Angels' total in scenarios where victory points are being used. The Blades of Reason may not be used against Necrons or Tyranids.
Blades of Reason
Source: Codex: Dark Angels, p. 17