By observables, do you mean what Scott Aaronson calls meat chauvinism? "My neighbor looks like me so he's conscious. A head of lettuce doesn't look like me, so it's not conscious." Isn't that a slippery slope? "That person has a different skin color than me therefore they are less human than I am." Such reasoning has been employed in the service of great evil throughout history. Can you explain what observables I should look for to determine whether my neighbor is conscious? Observables that could not equally well be used by a racist, for example, to deny someone's humanity. I don't mean to hijack the discussion from the original question of whether a head of lettuce may be conscious. I only mean to ask how I may determine, without relying on superficial appearances, how anything at all outside my own mind is conscious. See of course Alan Turing's brilliant 1950 analysis of this question. https://home.manhattan.edu/~tina.tian/CMPT420/Turing.pdf Of course Turing considers machines that may be hooked up to teletypes so as to communicate with people without giving away their physical appearance. But even that doesn't go far enough. Perhaps heads of lettuce don't communicate the same we we do, but have some sort of inner mental or emotional life. I did for a time reside in a rural area where I was obliged to learn a lot about insects, in order to keep them out of the house. I have no doubt in my mind that every insect in the world has a desire to live. If a being has a desire to live, it has some form of consciousness, however rudimentary. Plants strive to reach the sky. They wither and die without water. Can we call that desire? Are we so sure that it's not?