There are progressions in which the last step is sui generis — incommensurable with the others — and in which to go the whole way is to undo all the labour of your previous journey. ... Up to that point, the kind of explanation which explains things away may give us something, though at a heavy cost. But you cannot go on 'explaining away' for ever: you will find that you have explained explanation itself away. You cannot go on 'seeing through' things for ever. The whole point of seeing through something is to see something through it. It is good that the window should be transparent, because the street or garden beyond it is opaque. How if you saw through the garden too? It is no use trying to 'see through' first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To 'see through' all things is the same as not to see.