In light of that, I would say laying out agreed upon definitions would have to be allowable.
I would think DeWitt would say "yes of course" to that. I think he's saying that Epicurus was totally practical, accepting the good that comes through definition, while strenuously guarding against the bad that come can from it if not kept in check.
So many times this rings in my ears:
"And so it was that the lively force of his mind won its way, and he passed on far beyond the fiery walls of the world, and in mind and spirit traversed the boundless whole; whence in victory he brings us tidings what can come to be and what cannot, yea and in what way each thing has its power limited, and its deepset boundary-stone. And so religion in revenge is cast beneath men’s feet and trampled, and victory raises us to heaven."