nal and perishing existences and therefore the idea of a continued distinct existence must arise from the collaboration of qualities of objects and qualities of the imagination. If a sensation does not exist beyond our own perception, it cannot be a quality of continued existence. The two main qualities that are which we assume to be characterized by continued existence are constancy and coherence. Coherence is the regular dependence objects have on each other that produces the opinion of continued existence. Constancy is the instance when perceptions of external objects do not change when perception is interrupted. In order to maintain the regularity of operation, external objects require a continued existence.
It is typical for people to attribute a continued real existence to objects according to Hume. He describes the tendency to do this in four steps. One, the principle of identity is explained by stating that a single object conveys the idea of unity and number and not identity. Two, looking at the reasons why the resemblance of our broken and interrupted perceptions causes is to attribute an identity towards them. Three, explaining the need to bring together broken appearances by a continued existence. This is explained when the mind connects together the ideas of interrupted perceptions by the strong relations when distinct resemblances are observed in many different instances. Four, explaining the force of conception that arises from the need to link broken appearances. We have a need to assume continued existence of objects from memory and by coherence, without having experienced them in the past.
Hume then argues that the independent existence of our sensible experience is contrary to experience by stating that continued and independent existences are connected and dependent of each other. Therefore, our perceptions have no more a continued than an independent existence. The only existences that we are certain of are our perceptions because they are immediately presented to us by consciousness. Cause and effect can relate the existence of one thing to the existence of another because it shows a connection between them and shows that their existence is dependent on each other.
Hume discusses natural principles, which state that our sensible perceptions have a continued and interrupted existence. Reflected principles reject the opinion of natural principles that there is a thing in nature as a continued existence, which occurs when it is not in contact with the senses.
The tension between these two principles is that the imagination tells us that our resembling perceptions have a continued and undisturbed existence and they do not disappear with their absence. Reflection allows the idea that even our resembling perceptions are interrupted in their existence and are differ from each other. Hume carries this further by supporting skepticism by stating that "Trivial trials of the fancy conducted by false superstitions" cannot cause a solid or rational system of determining existence. According to Hume, it is impossible for any system to defend the understanding of our senses.