XV.  And if, when we admit that in respect of being the Cause the Father is greater than the Son, they should assume the premiss that He is the Cause by Nature, and then deduce the conclusion that He is greater by Nature also, it is difficult to say whether they mislead most themselves or those with whom they are arguing.  For it does not absolutely follow that all that is predicated of a class can also be predicated of all the individuals composing it; for the different particulars may belong to different individuals.  For what hinders me, if I assume the same premiss, namely, that the Father is greater by Nature, and then add this other, Yet not by nature in every respect greater nor yet Father—from concluding, Therefore the Greater is not in every respect greater, nor the Father in every respect Father?  Or, if you prefer it, let us put it in this way:  God is an Essence:  But an Essence is not in every case God; and draw the conclusion for yourself—Therefore God is not in every case God.  I think the fallacy here is the arguing from a conditioned to an unconditioned use of a term, Or as the schoolmen say the fallacy is, A dicto secundum quid ad dictum simpliciter, one of the many forms of Undistributed Middle Term.  Petavius, however (De Trin.. II., v., 12), pronounces the argument of this section unsatisfactory. to use the technical expression of the logicians.  For while we assign this word Greater to His Nature viewed as a Cause, they infer it of His Nature viewed in itself.  It is just as if when we said that such a one was a dead man they were to infer simply that he was a Man.