Can we know for sure that the external world exists? I was wondering about it for a while, and yesterday I thought that it must. You see, when I drink alcohol, it is an empirically experienced factor that affects my mind. That would mean that my mind is connected to my body. And because I can observe, smell and taste alcohol, that would be a proof that my senses can be trusted, at least to a degree on which they operate. Is that a valid argument?

You asked, "Can we know for sure that the external world exists?" That will depend, of course, on what's required for such knowledge. Some philosophers have said that such knowledge requires a successful proof of the existence of the external world, but many other philosophers (especially in the last few decades) have said that no such proof is required. For those who think a proof is required, G.E. Moore famously (or infamously) offered one: see this link. If you investigate Moore's proof at that link and in other places on the web, I think you'll get a sense of how the proof you offered might be received by various philosophers.

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