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Of liberty and necessity:
In this selection, Hume argues that what he calls liberty and necessity are compatible. In more familiar terms, we can understand him as arguing that determinism does not rule out human freedom. Hume recognizes that the question of whether liberty and necessity are compatible has been extremely contentious, but he maintains that disputes on this matter are largely disputes about the meanings of words. His project, then, is to provide clear understandings of the two concepts on which everyone can agree, and demonstrate that they are not in conflict with one another. Properly understood in this way, Hume thinks that in point of fact no one has ever held the position that necessity rules out human liberty, and that everyone has agreed that we both act by necessity and are at liberty in our behavior.
Hume begins by discussing the doctrine of necessity. Hume believes that we arrive at the notion of necessitation by observing over a period of time the constant conjunction of two types of events and inferring that one must be the cause of the other. Everyone believes, Hume thinks, that nature behaves according to necessitation of the kind that we infer; where certain kinds of causes occur, certain effects must follow (in the sense that those, and only those, effects follow from those causes). What remains to be seen is whether human activity is observed to adhere to the doctrine of necessity. Hume maintains that it does, observing that the same motives always produce the same actions: the same events flow from the same causes. Hume's evidence for this is our own present-day observations, as well as the observations of history. We are confident that people have always behaved as a result of certain emotions and motivations, and that these emotions and motivations (and their effects) have remained basically constant, so far as we can tell. We are so confident in this, Hume thinks, that if someone were to tell us of people who did not behave in these ways, we would simply assume that he is lying. Hume recognizes that there is still a great deal of variety in human action, even when motivation and circumstances are the same, but argues that this is no reason to suspect that human action is not necessitated. Rather, it is evidence that the mechanisms that determine human behavior are extremely complex. The fact that we are able to predict what people with whom we are familiar will do in certain circumstances should further count as evidence that their behavior follows regular laws.
The doctrine of liberty, Hume thinks, is also universally acknowledged as true. By liberty, Hume means a power of acting or not acting, according to the determinations of the will. Liberty, then, is the capacity that I have to act in accordance with what my will has selected. So, if I will to raise my arm, and am able to do so, it is said that I am at liberty to raise my arm. If I will to cross the street, am able to do so, it is said that I am at liberty to cross the street. And this kind of liberty, Hume says, everyone enjoys, unless of course they are physically restricted in some way. What's more, this kind of liberty is not in conflict with necessity. For I will still be capable of raising my arm, if I will to do so, even if I am necessitated in my willing and raising.
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