The only real threat to liberty is necessitation by external forces, as when a person is forced to do something she does not want to do.

The second source of resistance to compatibilism stems from confusion about necessity. People are prone to think that necessity rules out liberty because they conflate necessity with compulsion or force. They believe that when A causes B, A compels or forces B. Hume holds that this is a mistake, however. Causal necessity is nothing more than the “constant conjunction” of similar objects and a customary inference of the mind from the one to the other (EHU 8.1.5). For example, experience shows tha