The Moon Does Not Exist If No Humans 'Look' at It
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How humans are deceived by evolution to come to believe in bodies, or material objects [of the external world], that continue to exist at times when nobody perceives them
Views?In the Treatise section “Of scepticism with regard to the senses,” Hume tries to explain how we come to believe in bodies, or material objects, that continue to exist at times when nobody perceives them.
He thinks that this belief can take two different forms:
a “vulgar” or ordinary form, and
a “philosophical” form.
Hume thinks that the only things “present to the mind” are perceptions, or impressions and ideas (T 1.2.6.8, T Abs 5; SBN 67, 647).
But ordinarily, he thinks, we do not realize this.
Instead, we take certain of our sense-impressions to be bodies—that is, we ordinarily believe, of certain sense-impressions, that they continue to exist at times when they are not present to our minds (T 1.4.2.31, 1.4.2.36; SBN 202, 205).
Hume calls this “vulgar” belief “the fiction of a continu’d existence” (T 1.4.2.36; SBN 205).
According to Hume, the main reason why we entertain this “vulgar” fiction is the “constancy” of certain sense-impressions before and after an interruption in our experiences (T 1.4.2.23; SBN 198–9).
Suppose that I shut my eyes for a moment and that, upon re-opening them, I receive sense-impressions of the furniture in the room that closely resemble those that I received before shutting my eyes.
Because of this resemblance or “constancy,” when I recall the earlier impressions, I naturally recall the later impressions, too: my mind “readily passes from one to the other,” due to the association of ideas of resembling objects.
Thanks to a complicated imaginative mechanism, which Hume describes over several pages, this association of ideas leads me to imaginatively fill the gap in the sequence of sense-impressions that I received:
I imaginatively construct ideas of furniture existing during the time when my eyes were shut, connecting up my memories of the last furniture-impression that I received before shutting my eyes and the first one that I received after re-opening them (T 1.4.2.31–40; SBN 201–8).
Because these imaginatively constructed ideas are associated with memories, a high degree of force and vivacity is transmitted to them (T 1.4.2.41–42; SBN 208–9).
Thanks to this mechanism, which involves both the association of ideas and the transmission of force and vivacity among related perceptions, I ordinarily come to believe, of my furniture-impressions, that they continued to exist while my eyes were shut.
However, Hume argues that none of our sense-impressions continue to exist at times when they are not present to our minds (T 1.4.2.44–45; SBN 210–11).
When I shut my eyes, the furniture-impressions that were present to my mind cease to exist; when I re-open my eyes, new furniture-impressions are created in my mind, which are similar, but not numerically identical, to the earlier ones.
So, the “vulgar” fiction of a continued existence is false, according to Hume.
This is consistent with an interpretation on which Hume thinks that all fictions are falsehoods; however, it is also consistent with one on which Hume thinks that only some fictions are falsehoods, while others are unjustified beliefs or unintelligible pseudo-beliefs.
