42. These are both vital conditions of your healthy progress. On the one hand, observe that you do not wilfully use the realistic power of art to convince yourselves of historical or theological statements which you cannot otherwise prove; and which you wish to prove: — on the other hand, that you do not check your imagination and conscience while seizing the truths of which they alone are cognizant, because you value too highly the scientific interest which attaches to the investigation of second causes.