In the aftermath of the battle against Belron the Fiend, Caius had been hard at work improving his chances of surviving another battle such as that.
He went all in with his Erratic spell combinations. He realized that while named spells, with actual powerful effects in their own right, made more potent erratic combinations, they were also the most difficult to handle.
Even though he was now at the Fourth Circle, combining two spells hadn't become easier because the spells were stronger now and, as this was not something he was supposed to be doing, his body was not scaling with it. This meant, that the stronger Caius became, the more difficult it would be to make Erratic combinations.
However, he also realized he could cut down that difficulty a lot by simply using 'unnamed Spells'.
Named spells are powerful. They possess identities and are 'complete' and so, they vehemently reject combining with anything else.
