It is quite evident that existence can no more be — René Descartes

It is quite evident that existence can no more be separated from the essence of God than the fact that its three angles equal two right angles can be separated from the idea of a triangle, or than the idea of a mountain can be separated from the idea of a valley. Hence it is just as much of a contradiction to think of God (that is, a supremely perfect being) lacking existence (that is, lacking a perfection), as it is to think of a mountain without a valley.