Closing My Eyes

Two summers ago I was asked if I know if the external world exists when I close my eyes, before being told that I cannot know the answer.  How does someone respond to this accurately?  This may be an uncomfortable question for some, but it's not a difficult claim to counter deductively.  No one needs to fear it as some unanswerable question!  In Christopher Nolan's creative film Memento, the main character brushes up against this topic on a couple of occasions, including in an internal monologue near the end.  He says to himself, in his mind, "I have to believe in a world outside my own mind . . . I have to believe that when my eyes are closed, the world's still here.  Do I believe the world's still here?  Is it still out there?"  I know for sure that the answer is "Yes".

It was an HBU honors college student, unsurprisingly (I get so frustrated with a lot of these intellectually deficient people from the honors college), who told me that I can't know if the external world continues to exist when I close my eyes.  I know that I have a mind, that I have a body, and that my bodily senses are contacting something that is both material and external to them.  I do not know the actual appearance of either my body or the external world, but I know that both exist (I explain how I know these things elsewhere [1]).  I don't need to know the appearances to know that matter exists outside of my mind.  Solipsism, the belief that nothing besides my conscious mind exists or can be known to exist, is utter nonsense, because immaterial things like logic and truth do not depend on my mind for their necessary existence, and because I do know that matter exists.  While I cannot know the exact appearance of it, matter does objectively exist and it is not my consciousness.

When I close my eyes, my sense of hearing, sense of position (proprioception), sense of touch, sense of temperature (thermoception), sense of pain (nociception), and other senses do not vanish.  I still hear, feel, perceive temperature, can taste, and so on.  It is entirely erroneous to say that closing my eyes shuts down all other forms of sensory awareness, whether of my body or of the external world.  My other senses are separate from my sense of sight and can continue working even in its complete absence.  A blind person can still feel, smell, taste, and sense position, temperature, and pain.

The way that I know matter exists is not my sight.  If I had no senses other than my sense of sight, then not only would I have no actual basis for knowing if there is an external world to begin with (as seeing something doesn't mean it is outside of my mind, since I can perceive purely mental images as well), I would also truly not know if the external world exists when I close my eyes.  I would only know for sure that when I open my eyes I have visual perceptions of things outside of my mind, and that when I close my eyes I stop experiencing the sights of external objects.  No means of knowing if my sight deals with actual material objects or if the things I am perceiving exist when my eyes close would be available to me.

But since I do have physical senses that function even when I close my eyes, I know that for as long as I feel physical sensations it follows by necessity that matter exists.  For this reason I know that matter exists even when I close my eyes and do not visually perceive it.  It is therefore entirely irrational for me to entertain the thought that the external world does not exist when I close my eyes, regardless of what some may insist.  This challenge can be easily approached and answered--definitively.

[1].  See here:
A.  https://thechristianrationalist.blogspot.com/2017/07/dreams-and-consciousness.html
B.  https://thechristianrationalist.blogspot.com/2017/08/the-external-world.html
C.  https://thechristianrationalist.blogspot.com/2017/04/the-reliability-of-senses.html