What the first party means by necessity properly so called: removal of the power to act otherwise
Those who insist that every necessity properly so called conflicts with freedom mean by that phrase only a necessity that does more than determine the agent to act. It also removes his power not to act or to act otherwise; it puts him in a condition where he not only acts surely and infallibly but really cannot fail to act, and that not only in the composite sense but in the divided sense too.
Such a necessity would leave the agent, whether he is acting or is on the point of acting, without the kind of power not to act, or to act otherwise, that a seated man has to walk even while he sits, and a walking man has to sit even while he walks.
Latin
XVI. Etenim qui pertendunt omnem proprie dictam necessitatem cum libertate pugnare, per necessitatem proprie dictam eam duntaxat intelligunt per quam agens, non tantum ad agendum determinatur, sed etiam quae tollit ab eo potestatem non agendi, aut aliter agendi, sive quae constituit agentem in eo statu, ut non solum agat certo & infallibiliter, sed etiam revera non possit non agere; idque non tantum in sensu composito, sed etiam in sensu diviso: ac proinde quae facit ut agens, sive dum agit, sive dum est proxime ad agendum paratus, non habeat talem non agendi, sive aliter agendi potestatem, qualis est in sedente, etiam dum sedet, potestas ambulandi, & vicissim in ambulante sedendi potestas, etiam dum ambulat.