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?