How Can We Possibly Tell If It’s Conscious?

April 18, 2002 by Ray Kurzweil

At the Tucson 2002: Toward a Science of Consciousness conference, Ray Kurzweil addressed the question of how to tell if something is conscious. He proposed two thought experiments.

Excerpted from a slide presentation at Tucson 2002: Toward A Science of Consciousness
April 10, 2002
Thought Experiment 1: Create Ray 2

  • Make a copy of all the salient details of me.
  • Ray 2 has all of my memories, so he remembers having been me.
  • He recalls all of my memories.
  • If you meet him, you would be convinced he is Ray (he passes a “Ray Turing Test”).
  • You could do this while I was sleeping, so I may not even know about Ray 2.
  • If you tell me that we don’t need Ray 1 anymore, I may beg to differ.
  • I may come to believe in Ray 2′s existence, but I would consider him “someone else.”.
  • Ray 2′s continued existence does not represent immortality for me.
  • Copying me does not transfer my consciousness because I’m still here… Okay, so far so good.

    Thought Experiment 2: Gradual Replacement of Ray

  • Replace a tiny portion of my brain with its neuromorphic equivalent.
  • Okay, I’m still here… the operation was successful (eventually the nanobots will do this without surgery).
  • We know people like this already (e.g., people with cochlear implants, Parkinson’s implants, other neural implants).
  • Do it again… okay I’m still here… and again…
  • At the end of the process, I’m still here. There never was an “old Ray” and a “new Ray”. I’m the same as I was before. No one ever missed me, including me.
  • Gradual replacement of Ray results in Ray, so consciousness and identity appears to have been preserved.


  • “Ray at the end of the gradual replacement scenario” is entirely equivalent to Ray 2 in the mental porting scenario.
  • “Ray at the end of the gradual replacement scenario” is not Ray but someone else.
  • But in the gradual replacement scenario, when did Ray become someone else?
  • The gradual replacement scenario is entirely equivalent to what happens naturally:
    &nbsp&nbsp – Most of our cells turn over within a month or a few months.
    &nbsp&nbsp – Those that persist longer (e.g., neurons) nonetheless replace their particles.
  • So are we continually being replaced by someone else?

    This is a real issue wrg Cyronics

  • Assuming a “preserved” person is ultimately “reanimated,” many of the proposed methods imply that the reanimated person will be “rebuilt” with new materials and even entirely new neuromorphically equivalent systems.
  • The reanimated person will, therefore, effectively be “Ray 2” (i.e., someone else).

    There is no objective (third party) test for subjectivity (first person experience aka consciousness)

  • If Ray 2 happens to be nonbiological:
    &nbsp&nbsp– He would have all of the same abilities to understand his own situation, the same feedback loops.
    &nbsp&nbsp– The activity in his nonbiological brain would be comparable to Ray 1.
    &nbsp&nbsp– He would be completely convincing to Ray’s friends.
    &nbsp&nbsp– But there is no way to experience his subjective experiences without making philosophical assumptions.
  • Machines today are not convincing, but they are still much simpler than human intelligence.
  • But this gap will be closed, and future machines will be “convincing” in their emotional intelligence.
  • But there remains an inherent objective gap in assessing the subjective experience of another entity.

    The “Hard” Issue of Consciousness

  • Only becomes a scientific question when one makes certain philosophical assumptions.
  • Some people conclude that consciousness is an illusion, that there is no real issue.
  • Consciousness is, therefore, the ultimate ontological question, the appropriate province of philosophy and religion.
  • So my philosophy is…

    … Patternism

  • Our ultimate reality is our pattern.
  • Knowledge is a pattern as distinguished from mere information.
  • Losing knowledge is a profound loss.
    &nbsp&nbsp– Losing a person is a profound loss.
  • Patterns persist.
    &nbsp&nbsp– The pattern of water in a stream
    &nbsp&nbsp– Ray
  • We are still left with dilemmas because patterns can be copied

    We will ultimately come to accept that nonbiological entities can be (are) conscious

  • But this is a political and psychological prediction.
  • There is no way to demonstrate this without making philosophical assumptions

    You all seem conscious, but

  • Maybe I’m living in a simulation and you’re all part of the simulation.
  • Or (at the end of the conference), perhaps I only have memories of you, but the experiences never actually took place.
  • Or, maybe I am only having a conscious experience of recalling memories of you but neither you nor the memories really exist.
  • Or, perhaps…