Durandus answers his own objection: without grace a man would be damned for original sin alone
He first argues against his own view: 'No one is damned except for a sin of commission or omission. Whoever fulfils the precepts of the law omits nothing, and whoever avoids all evil commits nothing. So if man could fulfil the precepts without grace, he could avoid sin without grace, and so avoid damnation without grace. But whoever is not damned is in glory. So a man without grace could be in glory.'
His answer is that, even without any sin of omission or commission, man would be damned for original sin alone unless grace set him free.
Latin
XI. Postquam enim sic contra propriam sententiam argumentatus est, Nullus damnatur nisi pro peccato commissionis, vel omissionis: sed qui praecepta legis implet, nihil omittit: qui autem omne malum vitat, nihil committit: si igitur sine gratia praecepta legis homo possit implere, cum sine gratia possit peccatum vitare, tunc sine gratia posset homo vitare damnationem: sed qui non damnatur est in gloria: Ergo homo non habens gratiam posset in gloria esse. Respondet, quod absque peccato omissionis & commissionis damnaretur homo pro solo peccato originali, nisi per gratiam liberaretur.