Applied to sinners: inability is hardness of will
Thesis XX. Applying this to the case in hand, they say that the inability of sinners to carry out God's commands is such that they do not cease to be able to keep them if they choose. 'Let them will it,' they say, 'and will it fully, and the moment they have willed it the commands will be kept. If they will not, and therefore cannot, who would not hold against the unwilling the hardness of their wicked will and the loss of power that followed?
'In truth, lacking such power is nothing other than the hardness of a bad will; and being unable to retreat from a will once adopted is nothing other than willing stubbornly.' So Jansenius, that bishop of Ypres, philosophizes on the subject in De gratia Christi Salvatoris, book 3, chapter 15.
Latin
XX. Atque ut haec ad rem praesentem applicent, dicunt impotentiam divina mandata faciendi, quae in peccatoribus reperitur, esse talem, ut non desinant ea implere posse si voluerint. Velint enim, aiunt, pleneque velint, mox ut voluerint implebuntur: si autem nolint, ideoque non possint, quis nolentibus vitio non vertat duritiam iniquae voluntatis, secutumque defectum potestatis? Nam revera defectus talis potestatis non est aliud quam duritia malae voluntatis, a qua suscepta recedere non posse, non est aliud quam tenaciter velle. Sic hac de re Philosophatur Jansenius ille Episcopus Iprensis de Gratia Christi Salvatoris lib. 3. cap. 15.