So far is it from being lawfully inferred from this that lust is not sin that by necessary consequence its sinfulness can thence be elicited. The effect ought to correspond with the cause; nor could lust bring forth actual sin unless it is itself sin.

This very thing cannot be conceived, how something by way of an internal habit could be the cause of sin and not be sin. An internal cause inclining to act well is good.

Those who maintain that concupiscence is not sin, are wont to found on the passage of James, "Then, when lust has conceived, it bringeth forth sin," (James 1:15). But this is easily refuted: for unless we understand him as speaking only of wicked works or actual sins, even a wicked inclination will not be accounted sin. But from his calling crimes and wicked deeds the fruits of lust, and also giving them the name of sins, it does not follow that the lust itself is not an evil, and in the sight of God deserving of condemnation.

Once more, it is named, "lust" or "concupiscence"; which is sin itself, and the mother of all sin

The Reformed on the contrary state that all concupiscence, which certainly inclines toward evil, is sin, insofar as (1) all such concupiscence is against the law (Rom. 7:7) and thus is lawlessness, in which sin fully consists (1 John 3:4).