Thomas Nagel on Explanations"Dawkins and Atheism" in Secular Philosophy and the Religious Temperament (Oxford University Press: 2009), pp. 22-3.
The reason we are led to the hypothesis of a designer by considering both the watch and the eye is that these are complex physical structures that carry out a complex function, and we cannot see how they could have come into existence out of unorganized matter purely on the basis of the purposeless laws of physics. For the elements of which they are composed to have come together in just this finely tuned way purely as a result of physical and chemical laws would have been such an improbable fluke that we can regard it in effect as impossible: The hypothesis of chance can be ruled out. But God, whatever he may be, is not a complex physical inhabitant of the natural world. The explanation of his existence as a chance concatenation of atoms is not a possibility to which we must find an alternative, because that is not what anybody means by God. If the God hypothesis makes sense at all, it offers a different kind of explanation from those of physical science: explanation by the purpose or intention of a mind without a body, capable nevertheless of creating and forming the entire physical world. The point of the hypothesis is to claim that not all explanation is physical, and that there is a mental, purposive, or intentional explanation more fundamental even than the basic laws of physics, because it explains even them.
All explanations come to an end somewhere. The real opposition between Dawkins’s physicalist naturalism and the God hypothesis is a disagreement over whether this end point is purely physical, extensional, and purposeless, or whether it is mental, intentional, and purposive. On either view, this ultimate explanation is not itself explained. The God hypothesis does not explain the existence of God, and naturalistic physicalism does not explain the laws of physics.