  One possibility is that Hume thinks that we cannot interpret the continuing residence of a person in a state as a case of consent to the authority of the state because we have no reason to think that the continuing residence was chosen as a result of reflection on whether it constituted consent. The impoverished person who remains in the state in which he finds himself gave no thought whatsoever to any consideration other than that to move would be highly costly or otherwise unpleasant. We have no reason to think that he gave any thought to the question of consent and so it is illegitimate to interpret his behavior in that way.