deindent Sorry for kibitzing but I wanted to be fair to all points of view even those of the dualists so I tried to stick to presenting the thought experiments without drawing conclusions  The thought experiment is this   you have one observer  The observer gets cloned into copy  and copy  either HubertYorick or startrek style  The copies diverge either because of internal noise or because of the environment  From a third person point of view this is an objective description of the evolution of a physical system there is absolutely no ambiguity about what is going on one observer becomes two If probed each copy would say that they were the initial observer before the cloning event But viewed from the inside if you are the observer getting cloned there is a very natural question you can ask Am I going to end up being copy  or am I going to be copy  This question cannot even be formulated from the outside so it has no objective answer but it is subjectively very important if you are the observer  This scenario is Dennetts and to some extent Everetts Since the question doesnt even make sense when formulated in the third person perspective the answer to this question does not lie in the position and velocities of any atoms You might conclude that this question doesnt make any sense But in any case the answer to this question is  bit of subjective information which both copy  and copy  know and which the original observer does not In the objective third person view there is no information gained you know that copy  will say I am copy  and copy  will say I am copy   To give an example of actual OR and SYNTH Ill go beyond Dennetts example suppose that the copying goes on indefinitely so that the cloning keeps happening again and again Then it is very difficult to say what it feels like for the observer from the first person perspective For example take a startrek duplicator and duplicate the observer and then duplicate each duplicate but add a twist the duplicator keeps the data from the first duplication event in its memory banks and makes a third copy in the exact same state twenty years later and starts duplicating that observer too in the same way And then it does so again forty years later then sixty years later What is the subjective experience From a naive counting perspective I should predict that I would be nearly certainly teleported in time to some distant future point because the number of future copies of my present state is vastly greater than the two present copies On the other hand the total number of observers descended from the current duplicates will always outnumber the observers descended from the future duplicates So perhaps the right counting is by the number of descendents at each time slice rather than by the total number of descendents of my present state Even worse how can my subjective experience change depending on whether somebody millions of years in the future turns off the darned duplicator Boltzmanns brain is a similar idea