Pjileb 33c

καὶ τῷ νῷ πρὸς τὰ δευτερεῖα, ἐὰν μὴ πρὸς τὰ πρωτεῖα δυνώμεθα προσθεῖναι, προσθήσομεν.
This is quoted in LS still i do not get it: what do we add to what? Do we add to the mind? or to the second prize? Would it not be easier to delete the pros?