not to speak of a final cause
God is the final cause, and Mary Shelley would have been well aware that a great many people in England could purport to speak definitively on a subject from which Victor backs skeptically away. Victor is perhaps remembering that Newton in his last years wrote a two-volume commentary on the Book of Revelation, where the final cause, in the conventional teaching of Christianity, is cryptically revealed. The secondary and tertiary grades of causation would be, for example, the rationale behind the laws of the universe enunciated with such clarity by Isaac Newton. An example closer to the fictional point would be to understand why and how the Grand Unified Field operates, since both Victor Frankenstein and Robert Walton have been engaged in trying to fathom isolated aspects of it. See I:L1:2 and note.