Obj. 2:  Further, some sins are mortal in virtue of their species [*_Ex genere,_ genus in this case denoting the species], as murder and adultery; and some are venial in virtue of their species, as in an idle word, and excessive laughter.  Therefore venial and mortal sins differ specifically.

Obj. 3:  Further, just as a virtuous act stands in relation to its reward, so does sin stand in relation to punishment.  But the reward is the end of the virtuous act.  Therefore punishment is the end of sin.  Now sins differ specifically in relation to their ends, as stated above (A. 1, ad 1).  Therefore they are also specifically distinct according to the debt of punishment.

On the contrary, Those things that constitute a species are prior to the species, e.g. specific differences.  But punishment follows sin as the effect thereof.  Therefore sins do not differ specifically according to the debt of punishment.

I answer that, In things that differ specifically we find a twofold difference:  the first causes the diversity of species, and is not to be found save in different species, e.g. “rational” and “irrational,” “animate,” and “inanimate”:  the other difference is consequent to specific diversity; and though, in some cases, it may [follow from the diversity of species], yet, in others, it may be found within the same species; thus “white” and “black” are consequent to the specific diversity of crow and swan, and yet this difference is found within the one species of man.

We must therefore say that the difference between venial and mortal sin, or any other difference is respect of the debt of punishment, cannot be a difference constituting specific diversity.  For what is accidental never constitutes a species; and what is outside the agent’s intention is accidental (Phys. ii, text. 50).  Now it is evident that punishment is outside the intention of the sinner, wherefore it is accidentally referred to sin on the part of the sinner.  Nevertheless it is referred to sin by an extrinsic principle, viz. the justice of the judge, who imposes various punishments according to the various manners of sin.  Therefore the difference derived from the debt of punishment, may be consequent to the specific diversity of sins, but cannot constitute it.

Now the difference between venial and mortal sin is consequent to the diversity of that inordinateness which constitutes the notion of sin.  For inordinateness is twofold, one that destroys the principle of order, and another which, without destroying the principle of order, implies inordinateness in the things which follow the principle:  thus, in an animal’s body, the frame may be so out of order that the vital principle is destroyed; this is the inordinateness of death; while, on the other hand, saving the vital principle, there may be disorder in the bodily humors; and then there is sickness.  Now the principle of the entire moral order is the last end, which stands