The mind is probably not infinite, despite the internal sense that we can think any thought. Assuming some mapping from brain state to mind state, then there are really at most N=(# of neuron states)^(# of neurons) possible mind states. What thoughts lie outside the size |N| set and are thus unthinkable, or lie inside but are unreachable? If the mapping of brain states to mind states is not one to one, what brain states are phenomenally indistinguishable, and why?